Institute of Infectious Disease and Tropical Medicine, University of Milan, Luigi Sacco Hospital, Milan, Italy
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Keywords: HIV , HAART , immune reconstitution , immunotherapy , IL-2
![]() |
Rationale for immunotherapy in HIV infection |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
A fascinating strategy aiming at the broadest immune reconstitution, possibly overcoming the limitations of HAART, consists of the adjuvant use of immunomodulants. Thus far, several immune-based approaches have been investigated, and include cytokines that stimulate cell-mediated immunity, like interleukin (IL)-2, IL-12, IL-7 and IL-15,11 immunosuppressive drugs aiming at the containment of the immune hyperactivation known to characterize HIV immunopathogenesis, such as corticosteroids, hydroxyurea, ciclosporin A, mycophenolate mofetil and thalidomide,12 and compounds selectively targeting HIV-specific immunity, thus potentially enhancing direct anti-HIV cytotoxicity (e.g. tucaresol and murabutide).13,14
Thus far, IL-2 represents the most promising immunomodulant approach, and extensive work has been carried out, indeed proving its efficacy in significantly expanding the CD4 cell pool.11 However, several issues on the role of IL-2 in HIV disease have yet to be clarified, and include its functional effect, the population that would mostly benefit from IL-2, the best treatment schedule, the IL-2-driven immune reconstitution, and, most importantly, its actual clinical benefit.
![]() |
Open issues: assessing the correct place and role of adjuvant IL-2 in HIV disease |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Aside from the selective expansion of CD4 cells, several issues on the role of IL-2 in HIV disease have yet to be clarified, and include the role of IL-2 in functional immune enhancement, the population that would mostly benefit from IL-2, the best treatment schedule, and the IL-2-driven immune reconstitution. Above all, the key question remains whether the IL-2-mediated rise in CD4 cell count is indeed associated with an actual clinical benefit in terms of disease progression and death.
This latter issue is now being addressed in two large international, randomized clinical trials. More specifically, the International Study of Interleukin-2 in people with Low CD4+ T-Cell Counts on Active Anti-HIV Therapy (SILCAAT) was designed to investigate HIV-infected patients with CD4 cell counts of 50299/mm3 over 46 years. However, SILCAAT was discontinued by the sponsor in October 2002, and is now been continued for the patients enrolled, under the sponsorship of the National Institutes of Health.27 The second worldwide clinical trial, Evaluation of Subcutaneous Proleukin (Interleukin-2) in a Randomized International Trial, ESPRIT, is a National Institutes of Health-supported study of 4000 HIV-positive individuals with CD4 cell counts of at least 300/mm3 over a 5 year period.28 Within the next few years, these studies could hopefully provide the most important results to clarify the clinical benefit of adjuvant IL-2 in HIV infection.
Thus, while clinical end points are now under investigation, specific immunological end points have been addressed in Phase I/II trials, aiming at answering the open questions relative to the role of IL-2 in HIV disease, possibly laying the premises for more focused clinical trials.1724
Clinical setting
Thus far, no clear-cut consensus has been reached on the population(s) of HIV-infected individuals who will benefit the most from IL-2 immunotherapy, with the fittest treatment schedules, allowing for the maximum benefit and the minimum side effects. As for the IL-2 regimen, following initial studies using continuous intravenous high dose administration, several lines of evidence have now converged to the conclusion that lower dosages given subcutaneously in an intermittent fashion are equally effective in expanding CD4 cell counts.29 Furthermore, low dose, intermittent regimens are much better tolerated and display only transient interference with HIV viral replication.
With respect to the cohort of HIV-positive patients, even though IL-2 has been proposed for patients with high-to-moderate CD4 counts, aiming at the maintenance of an appropriate CD4 cell compartment, the actual rationale and clinical impact of adjuvant IL-2 in individuals with a quantitatively preserved T cell compartment are indeed still controversial and have yet to be defined.
Most interestingly, stronger evidence has been brought about for the use of IL-2 in patients who fail to restore the circulating CD4 cell compartment following long-term HAART, despite a marked reduction in virus load (immunological non-responders, INRs),5,6,30,31
and possibly in HAART-naive individuals with advanced disease. Indeed, results have been reported from several controlled studies evaluating IL-2 in INRs.2124
In particular, the safety, tolerability and immunological benefit of IL-2 plus HAART versus HAART alone was recently investigated in 22 INRs (CD4 cells 200/mm3; HIV-RNA
50 copies/mL following at least 12 months of stable HAART) enrolled in a controlled randomized trial.23
In this study, a low-dose prolonged intermittent IL-2 regimen was specifically chosen, consisting of three IL-2 cycles (one cycle: 3 x 106 IU once a day subcutaneously at days 15 and 812) for an overall duration of 10 weeks. The low dose prolonged intermittent IL-2 regimen was chosen with the specific aim of balancing tolerance with efficacy, on the basis of both ex vivo lymphocyte growth patterns observed in patients with cancer, displaying maximum increase after 23 weeks of treatment,3235
and in vivo data showing sustained immunological response and significantly lower toxicity when using low IL-2 dosages.21,29
The IL-2 regimen adopted proved safe, with only mild side effects, consisting of low-grade fever, mild constitutional symptoms, and reversible nodule at the site of IL-2 injection. Importantly, no substantial interference with HIV replication was seen. In terms of immunological efficacy,21,22,24
IL-2 resulted in a significant increase in CD4 cells > 100% versus baseline levels, sustained up to 1 year of follow-up, whereas HAART patients experienced a much less relevant and slower rise in CD4 cells (Figure 1a and b). Furthermore, clinical records of the patients enrolled suggested that the accelerated IL-2-driven CD4 cell gain might indeed be effective in preserving an adequate cellular immunity, as no HIV-related clinical events were observed among IL-2-treated patients, whereas more than 30% of HAART-alone patients presented minor opportunistic infections.23
Taken together, these findings demonstrate that low-dose prolonged intermittent IL-2 immunotherapy in INRs may exert an immunological effect in INRs, with a possible role also in preventing the onset of HIV-related clinical events, thus outweighing the IL-2-related side effects. However, results from larger ongoing clinical studies are needed to confirm these data.27,28
|
Furthermore, the use of IL-2 has also been recently proposed within structured treatment interruption (STI) protocols during both chronic disease and primary HIV infection (PHI).37 In particular, preliminary data reported that in chronically infected patients with CD4 cells > 500/mm3, the administration of IL-2 before HAART interruption results in a longer time before CD4 drop to the threshold for restarting therapy, indeed suggesting that, by prolonging the time off-therapy, an IL-2-based intervention may indeed enhance an HAART-sparing strategy.38,39 Moreover, IL-2 has also been proposed within STI protocols in patients treated with HAART during PHI, with the additional rationale here to selectively expand HIV-specific T cell clones, which have been shown to characterize the very early phases of HIV infection, and to be preserved by HAART initiation during PHI.40 Controlled studies evaluating IL-2 in these populations are ongoing41,42 (Marchetti, G., Cesari, M., Bandera, A., Trabattoni, D., Molteni, C., Schenal, M., Meroni, L., Moroni, M., Galli, M., Franzetti, F., Clerici, M. and Gori, A., unpublished data). These data, albeit preliminary, allow for the intriguing speculation of a possible role of IL-2 in sustaining a normal and functional CD4 cell compartment also in the context of STI protocols. Furthermore, for toxicity sake, the possibility of sparing antiretrovirals for longer time frames by administering IL-2, thus containing the heavy HAART-related long-term toxicity, is by itself an argument strong enough to justify the reversible IL-2-induced side effects.
IL-2-driven immune reconstitution
The hallmark of IL-2-driven immune reconstitution in HIV infection is the significant and sustained increase in CD4 cells. However, the specific immunological pathways involved in the IL-2-mediated CD4 cell expansion still remain somehow controversial, as well as the relationships with the pathogenetic mechanisms underlying the HIV-mediated immune deficits. Several hypotheses have been proposed, that include the contribution of peripheral proliferation and survival of existing cells,43,44 the rate of T cell apoptosis,45 de novo T cell synthesis by the thymus,23,46,47 or a combination of these factors. However, a comprehensive model of the immune pathways and T cell homeostatic balance featuring IL-2-mediated immune reconstitution is still missing.
These issues, combined with the description of IL-2-non-responders48 indicate that the IL-2-driven immune reconstitution is indeed quite a complex process, resulting from protean interactions with several mechanisms of T cell homeostasis translating in multiple immunological benefits, which go far beyond the mere quantitative expansion of CD4 cells. In particular, the possibility that IL-2 directly stimulates de novo T cell synthesis has important implications since this synthesis could favour the reconstitution of a more comprehensive immunity.
In this perspective, a deeper understanding of the effect of IL-2 on CD4 and CD8 cell dynamics and homeostasis, could provide an innovative framework for the most targeted and clinically advantageous IL-2-based strategies. Recently, several groups have extensively addressed this issue by combining T cell immune phenotyping, in vivo and ex vivo measurement of T cell proliferation and apoptosis, quantification of neothymopoiesis by T cell receptor excision circles (TRECs), and plasma IL-7 measurements, indeed allowing for a comprehensive picture of T cell immune recovery following adjuvant IL-2 in comparison with HAART alone.23,43,46,4952
Effect of IL-2 on T-lymphocyte proliferation and survival
Both enhanced T cell turnover and survival have been called upon as major mechanisms regulating the size of the peripheral T-lymphocyte pool following IL-2 immunotherapy.43
As for T cell proliferation, notwithstanding its role as the main T cell growth factor leading to the proliferation and differentiation of the whole T lymphocyte compartment, the hallmark of IL-2-driven immune reconstitution is the selective expansion of CD4 cells, ultimately resulting in the relative outgrowth of this subset. In particular, in INRs, IL-2 was shown to affect differentially the CD4 and CD8 cell subsets, with a preferential action on CD4 cells. Indeed, whereas HAART controls displayed a constrained yet parallel CD4 and CD8 cell recovery, IL-2 resulted in a more significant rise in CD4 than CD8 cell count (Figure 1ad), supporting the different regulation of CD4 and CD8 cell recovery during IL-2 immunotherapy. Since the peripheral T cell pool is maintained by both proliferation and renewal, the contribution of cell turnover and neothymopoiesis to both CD4 and CD8 cell subsets was also examined. IL-2 administration was associated with a significant rise in Ki67-proliferating CD4 cells, whereas no changes were seen in the CD8 cell pool (Figure 1e and f). Interestingly enough, at IL-2 discontinuation, a significant reduction was observed in CD4 cell turnover to below pre-treatment values (Figure 1e). Conversely, in HAART controls, the frequency of proliferating CD4 and CD8 was closely matched at all time-points (Figure 1f). These data confirm that CD4 and CD8 cells possess inherent biological differences,53
that become relevant under both endogenous and exogenous perturbations of physiological homeostasis like HIV infection itself or exposure to specific immune stimuli, such as IL-2.
Similar to the effect on peripheral T cell turnover kinetics, IL-2 was also associated with a significant long-term reduction in the percentage of activated CD38 CD8 cells,19,50 with possible implications in the containment of the immune activation-induced detrimental effects on HIV pathogenesis.10 Conversely, the CD8 activation status remained constantly elevated in HAART controls.
By confirming the selective activity of IL-2 on CD4 cells through a significant stimulation of peripheral proliferation during the period of IL-2 administration,43,45,49 these findings underline the efficacy of IL-2 in enhancing the most rapid and significant expansion of the highly exhausted CD4 cell pool in HIV disease. However, following cycle administration, IL-2 immunotherapy proved efficacious in lowering immune activation and CD4 cell proliferation, allowing for the speculation that the CD4 cell expansion during IL-2 follow-up is mainly maintained by increased survival of existing cells.44 Given these findings, decreases in turnover and prolonged survival in the periphery seem to be major mechanisms sustaining the IL-2-driven CD4 cell rescue in the long-term.
The possibility of immunotherapy to correct individual HIV-driven immune alteration, by exploiting the specific effects of different immunomodulants on T cell dynamics is indeed a fascinating and novel perspective in the treatment of HIV infection. In particular, the possibility that IL-2 contributes to the containment of T cell hyperactivation and proliferation allows us to view IL-2 treatment in HIV infection predominantly as immunotherapy targeting and reversing the HIV-driven generalized immune activation, with important pathogenetic and clinical implications.
Effect of IL-2 on T-lymphocyte apoptosis
Based on its critical role in the in vitro regulation of peripheral T cells,54,55
several groups have investigated the effect of IL-2 immunotherapy on T cell apoptosis rates, with somehow discordant results.45,56,57
In particular, the relative outgrowth of peripheral T cell turnover vis-à-vis to the actual CD4 cell gain during IL-2 cycles, give enough support to the hypothesis that elevated death rates accompany and indeed counterbalance the heightened T cell proliferation, still resulting in net CD4 cell expansion. According to the same model, it is also likely that the decreased T cell proliferation and activation observed in the IL-2 follow-up along with enhanced T cell survival might also lead to a parallel long-term reduction in T cell apoptosis.45
Taken together, these data indicate that the IL-2-driven consecutive balances in terms of death rates, proliferation and survival of the different subsets of T-lymphocytes determines the final effect on the T cell counts and phenotype. Indeed, immune phenotypic analysis of individual T cell subsets showed a discrepant pattern of recovery between IL-2 patients and HAART-alone controls. In particular, while HAART alone resulted in a preferential rescue of memory CD4 cells, with no changes in the naive compartment, IL-2 induced a significant and sustained expansion of both naive and memory CD4 cells,21,22,52,58 indeed reinforcing the potential of IL-2 to correct the HIV-driven imbalance within the naive/memory T cell pool, ultimately contributing to an overall rejuvenation of the T cell pool.
Effect of IL-2 on de novo T cell synthesis and IL-7/IL-7 receptor (IL-7R) system
As the IL-2-driven expansion of CD4 cells bearing a naive phenotype may indeed be derived from both peripheral expansion of existing cells and de novo T cell synthesis, the impact of neothymopoiesis on both CD4 and CD8 cell subsets was also studied. As for other parameters, CD4 and CD8 cells displayed a dichotomist trend, with a temporary tendency toward a rise in CD4 TRECs soon after IL-2 administration, possibly to an even higher extent in consideration of the high IL-2-driven proliferative dilution (Figure 1g and h).59
Conversely, no changes were detected within CD8 cells and in CD4 and CD8 TRECs in HAART controls (Figure 1g and h). These data indicate that the rise in naive CD4 cells induced by IL-2 does indeed reflect an increase in de novo T cell synthesis, proving the possible ability of IL-2 to stimulate thymic output, thus favouring the reconstitution of a most comprehensive immunity with a broad T cell receptor repertoire, which in turn could translate into a more efficient response to neoantigens.
Altogether, these data point to enhanced proliferation and prolonged survival of existing cells as the main mechanism responsible for IL-2-mediated CD4 cell recovery, and also suggest a boost of CD4 neothymopoiesis. Conversely, IL-2 failed to show an effect on both CD8 cell proliferation and activation in the periphery, thus implying that CD8 cells might follow different homeostatic dynamics,60 possibly peripheral distribution.
Aiming at a further understanding of the homeostatic effect of IL-2, the in vivo interactions between IL-2 and the IL-7/IL-7R system were also investigated,51 given the pivotal role of IL-7 in regulating both central and peripheral T cell homeostasis, and its effect on T cell survival and function.61 Compared with HAART alone, IL-2 induced a significant and sustained rise in IL-7 plasma levels, with no changes in IL-7R surface expression (Figure 2), indeed suggesting that in vivo IL-2 boosts IL-7 production without down-modulating its specific receptor, possibly preserving and enhancing IL-7-mediated T-lymphocyte homeostatic regulation. Altogether, the parallel expansion in total and naive CD4 cells, TRECs and IL-7 plasma levels makes it possible to envisage a model wherein IL-2 induced increased IL-7 production, which, in turn, orchestrated the cellular reconstitution by both neothymopoiesis and peripheral expansion (Figure 2). Furthermore, the recent observation that IL-2-non-responders display decreased IL-7R expression on both CD4 and CD8 cells also suggests that IL-7-mediated signalling is indeed critical in influencing the immunological response to IL-2 immunotherapy in HIV+ patients.48 By showing a bi-directional interaction between IL-2 and IL-7, these data confirm the existence of an important in vivo cross-talk between these two cytokines, both with central roles in T cell homeostasis regulation, with potential clinical implications.
|
Quality of IL-2-driven immune recovery
Role of IL-2 in functional immune enhancement
The issue regarding the role of IL-2 immunotherapy in functional immune enhancement in HIV infection is still quite controversial. In particular, in a randomized controlled trial in HAART-naive patients, Levy et al.62
demonstrated that the odds of being a responder to in vitro lymphocyte proliferative responses to recall antigens was significantly higher in IL-2 patients versus HAART-alone controls, allowing for the speculation that the CD4 cells expanded during IL-2 adjuvant therapy are indeed functional and able to support T cell function. Quite interestingly, Sullivan et al.63
demonstrated a significant rescue of lymphoproliferative responses to HIV-1-specific antigens during IL-2-associated viral breakthroughs. However, in contrast to these data, Valdez et al.64
were unable to demonstrate any immunization response (lymphoproliferative response, CD8 ELISPOT, in vivo antibody responses) to both recall and HIV-specific antigens following IL-2 administration.
Furthermore, the recent observation that IL-2 immunotherapy leads to the preferential expansion of naive and central memory CD4 cells, without affecting the effector pool44 has relevant potential functional implications.65 Indeed, whereas it is unlikely that the expanded memory pool is efficient in mounting a substantial immunity toward active infections, a future improvement of host defences against recall or even neoantigens might indeed be hypothesized, given the relative rarity of these challenges in adulthood. Moreover, the potential of IL-2 to directly stimulate neothymopoiesis further reinforces the role of IL-2 in selectively reconstituting neoantigen responses, given that TREC increases have indeed been correlated with improved neoantigen immune function.66
Combined, these data strongly indicate that the selective IL-2-driven expansion of specific T cell subsets does indeed also associate with a qualitative CD4 recovery, thus priming a tentative rescue of the HIV-related T-helper function imbalances. However, also under this perspective, clear cut answers on whether or not this will translate into clinical benefits as well as further speculation on the correct timing of IL-2 immunotherapy with respect to immunizations will hopefully be derived from ongoing Phase III trials.27,28
Role of IL-2 in immune tolerance
Aside from its role as a potent T cell growth factor, the actual functional activity of the CD4 cells expanded following IL-2 immunotherapy still remains to be clarified. Furthermore, both in vitro and in vivo animal models have shown that IL-2 is a master regulator of immune tolerance, via both the induction of Fas-mediated cell death and, most importantly, by promoting the development and peripheral expansion of CD4 CD25 regulatory T cells (Treg) which suppress in vivo excessive T cell responses.67
By bringing about a whole new perspective into the physiological function of IL-2, these observations also raise some concerns on the actual immunological effect of IL-2 immunotherapy, making it difficult to predict how it might affect in vivo interactions between proliferation and the suppressive phenotype of Tregs.68
The role and function of Tregs in the context of HIV infection have recently been investigated, yet remain quite controversial, with some preliminary data providing evidence that they may exert a detrimental effect by diminishing the HIV-specific T cell immune responses in vivo, possibly even hastening HIV disease progression.69
In contrast, an intriguing hypothesis proposes a possible positive effect of HIV-specific Treg cell-mediated suppressor function in the containment of several detrimental processes behind HIV pathogenesis, including activation-induced cell death and anergy, immune-mediated T cell destruction, and CD4 susceptibility to productive HIV infection, thus possibly delaying HIV disease progression.69
The enlightened understanding of the effect of IL-2 in specifically expanding and stimulating Treg cells in vivo combined with the most thorough investigation of Treg activity in HIV infection will allow for the most rational clinical manipulation of IL-2 signalling in HIV-infected patients.
![]() |
Conclusions and future directions |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
From a more mechanistic standpoint, IL-2-associated immune reconstitution results from protean interactions with T cell dynamics and homeostasis, consisting of a preferential effect on CD4 cells, through the sequential stimulation of peripheral T cell turnover, apoptosis, survival and possibly a boost of neothymopoiesis, with a significant effect also on IL-7 production. The potential of IL-2 to interact with thymic output and to reverse the HIV-mediated T cell homeostasis imbalances by modulating the in vivo dynamics of T-lymphocytes and regulatory cytokines, without substantially affecting HIV viral load, offers the appealing prospect of obtaining major immune reconstitution in the treatment of HIV disease, with possible relevant implications in terms of functional immune enhancement, as also suggested by several in vitro and ex vivo studies.6264,68 Furthermore, a deeper understanding of the tolerogenic effect of IL-2 immunotherapy in HIV infection with respect to its role in sustaining the pool and function of Treg cells will be of great help in the re-evaluation of how best to clinically manipulate IL-2 signalling strength.
Notwithstanding these encouraging data, any definitive conclusions on whether or not the IL-2-mediated immunological effects could indeed be exploited in the clinic, translating into a clear clinical benefit, as well as the clinical setting that could mostly benefit from IL-2, possibly even with a specific indication, inevitably depend on the results of the large Phase III studies that are currently under way.27,28 Indeed, the completion of these on-going clinical studies will certainly provide a more direct confrontation of areas of controversy vis-à-vis IL-2-driven immune expansion and clinical benefit.
Despite the intrinsic barriers to validating clinical benefit in large-scale clinical end point trials, the need for new and effective surrogate markers of immune function is now becoming a priority. Indeed, while CD4 cell count and plasma HIV-RNA levels can reasonably be considered as valid markers to evaluate response to HAART, other putative markers for immune recognition have thus far failed to show any meaningful relationship with future clinical outcome.70 This is particularly true when it comes to IL-2 immunotherapy, as the immunological benefits that it confers are indeed complex, and not necessarily reflected in a direct and unequivocal effect on CD4 cell count and HIV viraemia control.
![]() |
Acknowledgements |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
2
.
Ippolito, G., Galati, V., Serraino, D. et al. (2001). The changing picture of the HIV/AIDS epidemic. Annals of the New York Academy of Sciences 946, 112.
3 . Pitcher, C. J., Quittner, C., Peterson, D. M. et al. (1999). HIV-1-specific CD4+ T cells are detectable in most individuals with active HIV-1 infection, but decline with prolonged viral suppression. Nature Medicine 5, 51825.[CrossRef][ISI][Medline]
4 . Leibowitz, M. R. & Mitsuyasu, R. T. (2001). Immune reconstitution strategies in HIV. Current Infectious Disease Reports 3, 3028.[Medline]
5 . Piketty, C., Castiel, P., Belec, L. et al. (1998). Discrepant responses to triple combination antiretroviral therapy in advanced HIV disease. AIDS 12, 74550.[CrossRef][ISI][Medline]
6 . Renaud, M., Katlama, C., Mallet, A. et al. (1999). Determinants of paradoxical CD4 cell reconstitution after protease inhibitor-containing antiretroviral regimens. AIDS 13, 66976.[CrossRef][ISI][Medline]
7 . Connick, E., Lederman, M., Kotzin, B. et al. (2000). Immune reconstitution in the first year of potent antiretroviral therapy and its relationship to virologic response. Journal of Infectious Diseases 181, 35863.[CrossRef][ISI][Medline]
8 . Notermans, D., Pakker, N., Hamann, D. et al. (1999). Immune reconstitution after 2 years of successful potent antiretroviral therapy in previously untreated human immunodeficiency type-1 infected adults. Journal of Infectious Diseases 180, 10506.[CrossRef][ISI][Medline]
9 . Wu, H., Kuritzkes, D., McClernon, D. et al. (1999). Characterization of viral dynamics in human immunodeficiency virus type 1-infected patients treated with combination antiretroviral therapy: relationships to host factors, cellular restoration, and virologic end points. Journal of Infectious Diseases 179, 799807.[CrossRef][ISI][Medline]
10 . Douek, D. C. (2003). Disrupting T-cell homeostasis: how HIV-1 infection causes disease. AIDS Reviews 5, 1727.[Medline]
11
.
Lederman, M. M. & Valdez, H. (2000). Immune restoration with antiretroviral therapies: implications for clinical management. Journal of the American Medical Association 284, 2238.
12
.
Fumero, E., Garcia, F. & Gatell, J. M. (2004). Immunosuppressive drugs as an adjuvant to HIV treatment. Journal of Antimicrobial Chemotherapy 53, 4157.
13
.
Bahr, G. M. (2003). Non-specific immunotherapy of HIV-1 infection: potential use of the synthetic immunodulator murabutide. Journal of Antimicrobial Chemotherapy 51, 58.
14 . Gori, A., Trabattoni, D., Bandera, A. et al. (2004). Immunomodulation induced by tucaresol in HIV infection: results of a 16 week pilot Phase I/II trial. Antiviral Therapy 9, 60314.[Medline]
15 . Bagby, G. & Heinrich, M. (2000). Growth factors, cytokines, and the control of hematopoiesis. In Hematology Basic Principles and Practice, 3rd edn, pp. 154202. Churchill Livingstone, Philadelphia, PA, USA.
16
.
Kovacs, J. A., Vogel, S., Albert, J. M. et al. (1996). Controlled trial of interleukin-2 infusions in patients infected with the human immunodeficiency virus. New England Journal of Medicine 335, 13506.
17 . Davey, R. T., Jr, Chaitt, D. G., Albert, J. M. et al. (1999). A randomized trial of high- versus low-dose subcutaneous interleukin-2 outpatient therapy for early human immunodeficiency virus type 1 infection. Journal of Infectious Diseases 179, 84958.[CrossRef][ISI][Medline]
18 . Levy, Y., Capitant, C., Houhou, S. et al. (1999). Comparison of subcutaneous and intravenous interleukin-2 in asymptomatic HIV-1 infection: a randomised controlled trial. ANRS 048 study group. Lancet 353, 19239.[CrossRef][ISI][Medline]
19 . Hengge, U. R., Goos, M., Esser, S. et al. (1998). Randomized, controlled phase II trial of subcutaneous interleukin-2 in combination with highly active antiretroviral therapy (HAART) in HIV patients. AIDS 12, F22534.[CrossRef][ISI][Medline]
20
.
Davey, R., Murphy, R., Graziano, F. et al. (2000). Immunologic and virologic effects of subcutaneous interleukin-2 in combination with antiretroviral therapy. Journal of the American Medical Association 284, 1839.
21
.
Arnò, A., Ruiz, L., Juan, M. et al. (1999). Efficacy of low-dose subcutaneous interleukin-2 to treat advanced human immunodeficiency virus type 1 in persons with 250/µL CD4 T cells and undetectable plasma virus load. Journal of Infectious Diseases 180, 5660.[CrossRef][ISI][Medline]
22 . David, D., Nait-Ighil, L., Dupont, B. et al. (2001). Rapid effect of interleukin-2 therapy in human immunodeficiency virus-infected patients whose CD4 cell counts increase only slightly in response to combined antiretroviral treatment. Journal of Infectious Diseases 183, 7305.[CrossRef][ISI][Medline]
23 . Marchetti, G., Meroni, L., Varchetta, S. et al. (2002). Low-dose prolonged intermittent interleukin-2 adjuvant therapy: results of a randomized trial among human immunodeficiency virus-positive patients with advanced immune impairment. Journal of Infectious Diseases 186, 60616.[CrossRef][ISI][Medline]
24 . Katlama, C., Carcelain, G., Duvivier, C. et al. (2002). Interleukin-2 accelerates CD4 cell reconstitution in HIV-infected patients with severe immunosuppression despite highly active antiretroviral therapy: the ILSTIM studyANRS 082. AIDS 16, 202734.[CrossRef][ISI][Medline]
25 . Mitsuyasu, R. (2002). Immune therapy: non-highly active antiretroviral therapy management of human immunodeficiency virus-infected patients. Journal of Infectious Diseases 185, Suppl. 2, S11522.[CrossRef][ISI][Medline]
26 . Sereti, I. & Lane, H. C. (2001). Immunopathogenesis of human immunodeficiency virus: implications for immune-based therapies. Clinical Infectious Diseases 32, 173855.[CrossRef][ISI][Medline]
27 . SILCAAT study design. [Online.] http://www.iatec.com/index2.html (29 October 2004, date last accessed).
28 . ESPRIT IL-2 Trial. [Online.] http://www.espritstudy.org (29 October 2004, date last accessed).
29 . Tambussi, G., Ghezzi, S., Nozza, S. et al. (2001). Efficacy of low-dose intermittent subcutaneous interleukin (IL)-2 in antiviral drug-experienced human immunodeficiency virus-infected persons with detectable virus load: a controlled study of 3 IL-2 regimens with antiviral drug therapy. Journal of Infectious Diseases 183, 147684.[CrossRef][ISI][Medline]
30 . Autran, B., Carcelain, G., Li, T. S. et al. (1999). Restoration of the immune system with anti-retroviral therapy. Immunology Letters 66, 20711.[CrossRef][ISI][Medline]
31 . d'Arminio Monforte, A., Testori, V., Adorni, F. et al. (1999). CD4 cell counts at the third month of HAART may predict clinical failure. AIDS 13, 166976.[CrossRef][ISI][Medline]
32 . Barni, S., Lissoni, P., Cazzaniga, M. et al. (1995). A randomized study of low-dose subcutaneous interleukin-2 plus melatonin versus supportive care alone in metastatic colorectal cancer patients progressing under 5-fluorouracil and folates. Oncology 52, 2435.[CrossRef][ISI][Medline]
33 . Lissoni, P., Barni, S., Brivio, F. et al. (1995). Treatment of cancer-related thrombocytopenia by low-dose subcutaneous interleukin-2 plus the pineal hormone melatonin: a biological phase II study. Journal of Biological Regulators and Homeostatic Agents 9, 524.[ISI][Medline]
34 . Bordin, V., Giani, L., Meregalli, S. et al. (2000). Five-year survival results of subcutaneous low-dose immunotherapy with interleukin-2 alone in metastatic renal cell cancer patients. Urologia Internationalis 64, 38.[CrossRef][ISI][Medline]
35 . Lissoni, P., Bolis, S., Brivio, F. et al. (2000). A phase II study of neuroimmunotherapy with subcutaneous low-dose IL-2 plus the pineal hormone melatonin in untreatable advanced hematologic malignancies. Anticancer Research 20, 21035.[ISI][Medline]
36
.
Lange, C. G. & Lederman, M. M. (2003). Immune reconstitution with antiretroviral therapies in chronic HIV-1 infection. Journal of Antimicrobial Chemotherapy 51, 14.
37 . Lori, F., Maserati, R., Foli, A. et al. (2000). Structured treatment interruptions to control HIV-1 infection. Lancet 354, 2878.[ISI]
38 . Henry, K., Tebas, P., Cherng, D. et al. (2004). Interleukin-2 prior to stopping effective antiretroviral therapy prolongs time off treatment: initial results of a pilot study utilizing CD4+ T-cell count < 350 cells/mm3 as the threshold for restarting HAART. In Program and Abstracts of the Eleventh Conference on Retroviruses and Opportunistic Infections, San Francisco, CA, 2004. Abstract 510, p. 248. Foundation for Retrovirology and Human Health, Alexandria, VA, USA.
39 . Katzenstein, D., Henry, K., Tebas, P. et al. (2004). Interrupting antiretroviral therapy (ART) using CD4+ T-cell counts < 350/mm3 to restart HAART (ACTG A5102). In Program and Abstracts of the XV International AIDS Conference, Bangkok, Thailand, 2004. Abstract TuPeB4585, p. 364. International AIDS Society, Geneva, Switzerland.
40 . Rosenberg, E. S., Altfeld, M., Poon, S. H. et al. (2000). Immune control of HIV-1 after early treatment of acute infection. Nature 407, 5236.[CrossRef][ISI][Medline]
41 . Hecht, F., Kahn, J., Martinez-Marino, B. et al. (2002). Interleukin-2 (IL-2) added to HAART in primary HIV infection enhances anti-HIV immune responses. In Program and Abstracts of the Ninth Conference on Retroviruses and Opportunistic Infections, Seattle, WA, 2002. Abstract 527-M, p. 249. Foundation for Retrovirology and Human Health, Alexandria, VA, USA.
42 . Hecht, F., Hare, C., McGrath, M. et al. (2003). Interleukin-2 in conjunction with HAART in early HIV infection increases naive and memory CD4 cells and lowers activation markers. In Program and Abstracts of the Tenth Conference on Retroviruses and Opportunistic Infections, Boston, MA, 2003. Abstract 649, p. 290. Foundation for Retrovirology and Human Health, Alexandria, VA, USA.
43
.
Natarajan, V., Lempicki, R. A., Sereti, I. et al. (2002). Increased peripheral expansion of naive CD4+ T cells in vivo after IL-2 treatment of patients with HIV infection. Proceedings of the National Academy of Sciences USA 99, 107127.
44
.
Sereti, I., Anthony, K. B., Martinez-Wilson, H. et al. (2004). IL-2-induced CD4+ T-cell expansion in HIV-infected patients is associated with long-term decreases in T-cell proliferation. Blood 104, 77580.
45 . Sereti, I., Herpin, B., Metcalf, J. et al. (2001). CD4 T cell expansions are associated with increased apoptosis rates of T lymphocytes during IL-2 cycles in HIV infected patients. AIDS 15, 176575.[CrossRef][ISI][Medline]
46 . De Paoli, P., Bortolin, M., Zanussi, S. et al. (2001). Changes in thymic function in HIV-positive patients treated with highly active antiretroviral therapy and interleukin-2. Clinical and Experimental Immunology 125, 4406.[CrossRef][ISI][Medline]
47 . Carcelain, G., Saint-Mezard, P., Altes, H. K. et al. (2003). IL-2 therapy and thymic production of naive CD4 T cells in HIV-infected patients with severe CD4 lymphopenia. AIDS 17, 84150.[CrossRef][ISI][Medline]
48 . Sereti, I., Sklar, P., Ramchandani, M. et al. (2004). Increased immune activation is associated with decreased responsiveness to in vivo IL-2 administration. In Program and Abstracts of the Eleventh Conference on Retroviruses and Opportunistic Infections, San Francisco, CA, 2004. Abstract 213, p. 143. Foundation for Retrovirology and Human Health, Alexandria, VA, USA.
49
.
De Paoli, P., Zanussi, S., Simonelli, C. et al. (1997). Effects of subcutaneous interleukin-2 therapy on CD4 subsets and in vitro cytokine production in HIV+ subjects. Journal of Clinical Investigation 100, 273743.
50 . Marchetti, G., Meroni, L., Molteni, C. et al. (2004). Interleukin-2 immunotherapy exerts a differential effect on CD4 and CD8 T cell dynamics. AIDS 18, 2116.[CrossRef][ISI][Medline]
51 . Marchetti, G., Meroni, L., Molteni, C. et al. (2004). IL-7/IL-7 receptor system regulation following IL-2 immunotherapy in HIV-infected patients. Antiviral Therapy 9, 44752.[Medline]
52 . Boutboul, F., Puthier, D., Nguyen, C. et al. (2003). Systematic microarray analysis reveals counter balance between perforin and interleukin 7 receptor with progression of HIV infection. In Program and Abstracts of the Tenth Conference on Retroviruses and Opportunistic Infections, Boston, MA, 2003. Abstract 34, p. 69. Foundation for Retrovirology and Human Health, Alexandria, VA, USA.
53 . Mackall, C. L., Hakin, F. T. & Gress, R. E. (1997). T-cell regeneration: all repertoires are not created equal. Immunology Today 18, 24551.[CrossRef][ISI][Medline]
54
.
Ku, C. C., Murakami, M., Sakamoto, A. et al. (2000). Control of homeostasis of CD8+ memory T cells by opposing cytokines. Science 288, 6758.
55 . Lenardo, M., Chan, K. M., Hornung, F. et al. (1999). Mature T lymphocyte apoptosisimmune regulation in a dynamic and unpredictable antigenic environment. Annual Review of Immunology 17, 22153.[CrossRef][ISI][Medline]
56 . Caggiari, L., Zanussi, S., Bortolin, M. et al. (2000). Effects of therapy with highly active antiretroviral therapy (HAART) and IL-2 on CD4+ and CD8+ lymphocyte apoptosis in HIV+ patients. Clinical and Experimental Immunology 120, 1016.[CrossRef][ISI][Medline]
57 . Pandolfi, F., Pierdominici, M., Marziali, M. et al. (2000). Low-dose IL-2 reduces lymphocyte apoptosis and increases naive CD4 cells in HIV-1 patients treated with HAART. Clinical Immunology 94, 1539.[CrossRef][ISI][Medline]
58 . Natarajan, V., Bosche, M., Metcalf, J. et al. (1999). HIV-1 replication in patients with undetectable plasma virus receiving HAART. Highly active antiretroviral therapy. Lancet 353, 11920.[ISI][Medline]
59 . Hazenberg, M., Verschuren, M., Hamann, D. et al. (2001). T cell receptor excision circles as markers for recent thymic emigrants: basic aspects, technical approach, and guidelines for interpretation. Journal of Molecular Medicine 79, 63140.[CrossRef][ISI][Medline]
60
.
Mackall, C., Fleisher, T., Brown, M. et al. (1997). Distinctions between CD8+ and CD4+ T-cell regenerative pathways result in prolonged T-cell subset imbalance after intensive chemotherapy. Blood 89, 37007.
61
.
Fry, T. & Mackall, C. (2002). Interleukin-7: from bench to clinic. Blood 99, 3892904.
62 . Levy, Y., Durier, C., Krzysiek, R. et al. (2003). Effects of interleukin-2 therapy combined with highly active antiretroviral therapy on immune restoration in HIV-1 infection: a randomized controlled trial. AIDS 17, 34351.[CrossRef][ISI][Medline]
63 . Sullivan, A., Hardy, G., Nelson, M. et al. (2003). Interleukin-2 associated viral breakthroughs induce HIV-1-specific CD4 T cell responses in patients on fully suppressive highly active antiretroviral therapy. AIDS 17, 6289.[CrossRef][ISI][Medline]
64 . Valdez, H., Mitsuyasu, R., Landay, A. et al. (2003). Interleukin-2 induces increases in CD4+ lymphocyte numbers but does not enhance responses to immunization: results of A5046s. Journal of Infectious Diseases 187, 3205.[CrossRef][ISI][Medline]
65 . Sallusto, F., Lenig, D., Forster, R. et al. (1999). Two subsets of memory T lymphocytes with distinct homing potentials and effector functions. Nature 401, 70812.[CrossRef][ISI][Medline]
66 . Markert, M. L., Hicks, C. B., Bartlett, J. A. et al. (2000). Effect of highly active antiretroviral therapy and thymic transplantation on immunoreconstitution in HIV infection. AIDS Research and Human Retroviruses 16, 40313.[ISI][Medline]
67
.
Nelson, B. H. (2004). IL-2, regulatory T cells, and tolerance. Journal of Immunology 172, 39838.
68 . Blattman, J., Grayson, J., Wherry, E. et al. (2003). Therapeutic use of IL-2 to enhance antiviral T-cell responses in vivo. Nature Medicine 9, 5407.[CrossRef][ISI][Medline]
69
.
Kinter, A. L., Hennessey, M., Bell, A. et al. (2004). CD25+CD4+ regulatory T cells from the peripheral blood of asymptomatic HIV-infected individuals regulate CD4+ and CD8+ HIV-specific T cell immune responses in vitro and are associated with favourable clinical markers of disease status. Journal of Experimental Medicine 200, 33143.
70 . Lederman, H. M., Williams, P. L., Wu, J. W. et al. (2003). Incomplete immune reconstitution after initiation of highly active antiretroviral therapy in human immunodeficiency virus-infected patients with severe CD4+ cell depletion. Journal of Infectious Diseases 188, 1794803.[CrossRef][ISI][Medline]
|