In this study, a higher proportion of men than women were non-Hispanic whites (51% vs 27%), and a higher proportion of women than men were non-Hispanic blacks (52% vs 31%). However, we found no evidence for an association between race/ethnicity and change in CD4 cell count after initiation of ART, indicating that race/ethnicity is not a confounder of the association between the other covariates and CD4 cell count change.
We also assessed the effect of baseline CD4 cell characteristics on the increase in CD4 cell count after initiation of therapy. In the 623 subjects who had comprehensive immunologic assessments, subjects with a higher baseline naive CD4 cell percentage had a greater increase in CD4 cell count at all time points, although the correlation coefficient was small (eg, r = 0.26 at week 48; P < 0.0001). Subjects who had a higher baseline naive/memory CD4 cell count ratio had a significantly greater CD4 cell count increase at all study time points (eg, r = 0.26 at wk 48; P < 0.0001). Younger age correlated with greater baseline naive CD4 cell percentage (r = −0.33) and naive/memory CD4 cell count ratio (r = −0.32) (both P values < 0.0001). For example, subjects aged 40 years or younger had a median naive/memory CD4 cell count ratio of 0.66 as compared with 0.36 for subjects aged older than 40 years (P < 0.0001). There was no evidence for a difference in baseline naive CD4 cell count or percentage between men and women.
We also examined the effect of baseline VL on the change in CD4 cell count. A higher baseline VL was associated with a greater increase in CD4 cell count through week 144. Subjects with higher baseline VL had lower baseline CD4 cell counts (r = −0.57; P < 0.0001). Even after adjustment for age, sex, baseline CD4 cell count, VS status, and initial treatment assignment, higher baseline VL remained associated with greater increase in CD4 cell count through week 144.
Virologic Response to Treatment and CD4 Cell Recovery
After initiation of ART, lower post-treatment VL, greater VL decline, and VS (VL ≤ 50 copies/mL) were associated with greater CD4 cell count gain in univariate regressions. In a multiple regression model that included age, sex, baseline CD4 cell count, baseline VL, and initial treatment assignment, VS was associated with greater CD4 cell count increase after adjustment for the other factors.
When we assessed immunologic recovery as a function of VS status (VL ≤ 50 copies/mL), we found a substantial proportion of subjects who had a lag between VS and achievement of an immunologic response (IR), defined as an increase from baseline in CD4 cell count of greater than 100/mm3. For example, at week 24, of the 608 subjects who had VS, 255 (42%) did not have an IR. Fifty percent of those subjects who had VS but not an IR at week 24 and who maintained VS at week 48 had an IR at week 48. With continued VS, the rate of IR increased among 148 subjects who maintained VS from weeks 24 to 144; 87% achieved an IR at week 144. Nevertheless, even after this prolonged VS, 13% of the subjects did not have an IR. Among the subjects who maintained VS from week 24 to 144, those who achieved an IR were younger than those who did not (median age, 35 vs 42 years; P = 0.005); among these subjects, there were no differences in sex, race/ethnicity, or injection drug use history in the immunologic responders versus nonresponders.
Initial Treatment Assignment and Immunologic Recovery
By intent-to-treat analysis, initial treatment assignment did not affect the CD4 cell count increase at week 96 (because a substantial proportion of subjects had changed therapy by week 144, we did not assess the effect of initial treatment assignment on CD4 cell count at this time point). When the analysis was limited to subjects on their first regimen, there was also no difference in CD4 cell count by treatment arm through week 144 (data not shown).
We found no evidence for a difference in the increase in CD4 cell count through week 144 in subjects assigned to the 2 different nucleoside backbones in this study: stavudine/didanosine or zidovudine/lamivudine (Fig. 2A). There was a significantly higher increase in median CD4 cell percentage in subjects randomized to initiate a zidovudine/lamivudine-containing regimen as compared with those who started with a stavudine/didanosine-containing regimen, although the differences were small (eg, at week 48, median increases of 8% vs 7%, respectively; P < 0.0001).
We also examined whether CD4 cell count recovery differed between subjects randomized to initiate therapy with a nelfinavir-containing regimen, an efavirenz-containing regimen, or a regimen containing both drugs. We found no evidence for a difference in the total CD4 cell count and the increase in CD4 cell count in these 3 groups (Fig. 2B).
Naive and Memory CD4 Cells After Starting ART
In the first few months after initiation of ART, there is typically an early increase in the number of memory CD4 cells followed by a slower rise in naive CD4 cells.8-10 In the 623 subjects who had comprehensive immunologic assessments, we found that the number of both memory and naive CD4 cells continued to increase at week 144, with no evidence of a plateau (Fig. 3A). Although there was a greater increase in the memory than in the naive CD4 cell count (median increase, 159 and 116, respectively, at week 144; P = 0.001), the fold increase in naive CD4 cells was greater than that in memory CD4 cells (median, 2.2- and 1.9-fold, respectively; P = 0.004). When we assessed the percentage of naive and memory CD4 cells, there was an increase in the percent naive cells for the first 48 weeks of therapy (P < 0.0001), whereas the percent memory cells declined slightly during this same interval (P = 0.002) (Fig. 3B). We found no evidence of any difference between the initial regimens in their effect on change in naive/memory CD4 cell count or percentage (data not shown).
T-Cell Activation After Initiation of ART
Uncontrolled HIV-1 infection is associated with high levels of T-cell activation,11,12 perhaps because of the enormous amounts of circulating viral antigen and immune dysregulation induced by CD4 cell depletion. In the 623 subjects who had measurements of lymphocyte activation, there was a rapid decline in activated T-cell percentage for the first 24 weeks of treatment (Fig. 4). The absolute CD8 cell count and the percent activated CD8 cells both declined in the first 24 weeks after initiation of therapy, and the changes in the 2 measures were correlated (eg, r = 0.32; P < 0.0001 at week 24). There was a greater decline in percent activated CD8 than in percent activated CD4 cells (median decrease, −19% vs −6%, respectively, at week 24); however, percent activated CD8 cells before therapy was higher than percent activated CD4 cells (49% vs 14%). Thus, at week 24, the median fold decrease in activated CD4 cell percentage was slightly greater than that in activated CD8 cell percentage (1.89- and 1.67-fold, respectively; P = 0.057). In subjects who had suppressed VL from weeks 24 to 144, the median percent activated CD4 cells was 6, and the median percent activated CD8 cells was 19.5 at week 144. We found no evidence that any of the 6 initial treatment regimens differed in their effect on reducing the percentage of activated CD4 or CD8 cells at week 144 (data not shown).
We also examined the effect of T-cell activation-as assessed by cell surface expression of both CD38 and HLA-DR-on change in CD4 cell count after starting therapy. Subjects with higher baseline percent CD8 cell activation had a greater increase in CD4 cell count from baseline to week 48 (r = 0.09; P = 0.04), but this effect was no longer statistically significant at subsequent weeks. We found no evidence for an association between baseline CD4 cell activation and change in CD4 cell count after ART initiation. In contrast, subjects who had higher levels of CD4 or CD8 cell activation after starting ART had smaller increases in CD4 cell count. For example, higher CD8 cell activation at week 48 was associated with lower CD4 cell count increases at week 48 (r = −0.13; P = 0.001). A higher activated CD4 percentage at week 48 was also associated with a lower CD4 cell count increase at week 48 (r = −0.20, P < 0.0001). The association between higher CD4 cell activation and lower change in CD4 cell count was seen even when the analysis was restricted to subjects who achieved an undetectable VL (≤50 copies/mL) at the time point for which the CD4 cell count was examined (data not shown). When the analysis was restricted to subjects who achieved an undetectable VL, the association between higher CD8 cell activation and lower change in CD4 cell count was statistically significant only at week 96 (data not shown).
When the association between CD4 cell recovery and expression of CD38 and HLA-DR were examined separately, we found that the percentage of CD38+ CD4 and CD8 T-cells at baseline was more strongly associated with CD4 cell reconstitution than the percentage of HLA-DR+ CD4 and CD8 cells (data not shown).
In this large prospective study of HIV-1-infected antiretroviral-naive subjects, we found that there was a steady rise in CD4 cell count after initiation of ART. Age of 40 years or younger, female sex, higher baseline naive/memory CD4 cell count ratio, and higher baseline VL were associated with a greater increase in CD4 cell count. Age, sex, and baseline VL were associated with CD4 cell rise even after adjusting for VS in a multiple regression model, indicating that there are factors that impact CD4 cell reconstitution after initiation of ART in addition to control of viremia. As expected, VS to 50 copies/mL or less was consistently associated with greater CD4 cell recovery. Although most subjects who maintained an undetectable VL had substantial immunologic recovery, 13% did not have a rise in CD4 cell count of greater than 100 cells/mm3 even after 144 weeks of VS. We did not find evidence that initial antiretroviral treatment assignment in this study affected total CD4 cell count recovery, reconstitution of naive/memory CD4 cells, or decline in T-cell activation.
In addition to recovering CD4 cells, subjects had a large increase in B-cell numbers after starting ART. HIV-1 infection impairs B-cell survival and function,13 perhaps by stimulating activation-induced cell death. Thus, suppression of viral replication may lead to improved B-cell survival and restoration of B-cell counts. This B-cell recovery may contribute to improved humoral immunity in HIV-1-infected patients who are successfully treated with ART.14
Many of the factors associated with greater CD4 cell recovery in this large prospective randomized study are consistent with findings in smaller retrospective or nonrandomized studies. Most studies suggest that younger subjects have a greater increase in CD4 cell count after therapy than older individuals.15 This may be because of the fact that younger individuals have a higher naive CD4 cell percentage and a higher naive/memory CD4 cell count ratio than older people, perhaps because of greater thymic function. In this study, HIV-1-infected subjects with a higher naive/memory CD4 cell ratio had a greater rise in CD4 cell count after ART. A similar finding has been seen in CD4 cell recovery after chemotherapy in subjects with cancer.16 These findings suggest that the CD4 naive/memory cell count ratio may be a general measure of the capacity for CD4 cell regeneration, although this must be confirmed in other studies.
The association between sex and CD4 cell recovery after ART is controversial.17-19 We found that women have a greater rise in CD4 cell count than men; this difference is statistically significant at week 48 and persists through week 96. Women in this study had higher baseline CD4 cell counts than men, but the association between sex and CD4 cell recovery persisted even after adjusting for baseline CD4 cell count (and for baseline VL, age, viral suppression, and treatment arm). One explanation for our findings is that women may normally have higher CD4 cell counts than men. In a study of HIV-1-negative individuals, women had approximately 100 more CD4 cells/mm3 than men; this number may be affected by estrogen and other hormonal influences.20 By suppressing HIV-1 replication, ART may lead to a greater increase in CD4 cell counts in women than in men because the normal homeostatic regulation of CD4 cell number is restored.
An important finding of ACTG 384 is that initial treatment assignment did not affect CD4 cell recovery, nor did it affect reconstitution of naive/memory CD4 cell subsets. Unlike other studies, we did not find evidence that different nucleoside backbones were associated with variable rises in CD4 cell count.2-5 Also, regimens that contained the protease inhibitor nelfinavir led to comparable CD4 cell gains as regimens containing the nonnucleoside reverse transcriptase inhibitor, efavirenz; combinations that included both did not lead to better CD4 cell recovery. Virologic suppression seems to be the most important treatment-related factor associated with CD4 cell count rise.
This study also demonstrates that both naive and memory CD4 cells are substantially regenerated in HIV-1-infected subjects who receive ART. In the first few months after initiating ART, there is a rapid increase in the number of memory CD4 cells followed by a slower rise in naive CD4 cells.8-10 In the current study, CD4 cell subsets were first assessed 6 months after treatment initiation, so we may have missed early changes. However, by 6 months after starting therapy, both naive and memory CD4 cell subsets had increased. Although the rise in the absolute numbers of memory CD4 cells was greater, the fold increase in naive CD4 cells exceeded that of memory CD4 cells. In fact, the percent memory CD4 cells declined slightly during the first year of therapy, whereas the percent naive CD4 cell increased. This finding suggests that ART leads to reconstitution of CD4 cells capable of responding to new antigens, which is consistent with the clinical improvement in most subjects who receive treatment.21
Finally, the results of this study add to accumulating data that persistent T-cell activation is associated with impaired immune regeneration.22 Excessive T-cell activation has been implicated in the pathogenesis of the CD4 cell depletion induced by HIV-1, perhaps through activation-induced cell death and impaired CD4 regeneration.11,12 Even after prolonged VS, the median percent activated CD4 and CD8 cells in subjects in this study remained higher than that seen in HIV-uninfected subjects.23 Whether pharmacologic reduction of T-cell activation will improve CD4 cell recovery is not known and is the subject of ongoing investigations.
The authors thank Meghan Geary, Minya Pu, Jessica Hass, Barbara Brizz, Bernadette Jarocki, and Jennifer Nowak for their invaluable assistance.
1. Lange CG, Lederman MM. Immune reconstitution with antiretroviral therapies in chronic HIV-1 infection. J Antimicrob Chemother
2. Eron JJ Jr, Murphy RL, Peterson D, et al. A comparison of stavudine, didanosine and indinavir with zidovudine, lamivudine and indinavir for the initial treatment of HIV-1 infected individuals: selection of thymidine analog regimen therapy (START II). AIDS
3. Squires KE, Gulick R, Tebas P, et al. A comparison of stavudine plus lamivudine versus zidovudine plus lamivudine in combination with indinavir in antiretroviral naive individuals with HIV infection: selection of thymidine analog regimen therapy (START I). AIDS
4. Landay AL, Spritzler J, Kessler H, et al. Immune reconstitution is comparable in antiretroviral-naive subjects after 1 year of successful therapy with a nucleoside reverse-transcriptase inhibitor- or protease inhibitor-containing antiretroviral regimen. J Infect Dis
5. van Leth F, Wit FW, Reiss P, et al. Differential CD4 T-cell response in HIV-1-infected patients using protease inhibitor-based or nevirapine-based highly active antiretroviral therapy. HIV Med
6. Robbins GK, De Gruttola V, Shafer RW, et al. Comparison of sequential three-drug regimens as initial therapy for HIV-1 infection. N Engl J Med
7. Shafer RW, Smeaton LM, Robbins GK, et al. Comparison of four-drug regimens and pairs of sequential three-drug regimens as initial therapy for HIV-1 infection. N Engl J Med
8. Autran B, Carcelain G, Li TS, et al. Positive effects of combined antiretroviral therapy on CD4+ T-cell homeostasis and function in advanced HIV disease. Science
9. Pakker NG, Notermans DW, de Boer RJ, et al. Biphasic kinetics of peripheral blood T-cells after triple combination therapy in HIV-1 infection: a composite of redistribution and proliferation. Nat Med
10. Bucy RP, Hockett RD, Derdeyn CA, et al. Initial increase in blood CD4(+) lymphocytes after HIV antiretroviral therapy reflects redistribution from lymphoid tissues. J Clin Invest
11. Hazenberg MD, Hamann D, Schuitemaker H, et al. T cell depletion in HIV-1 infection: how CD4+ T-cells go out of stock. Nat Immunol
12. McCune JM. The dynamics of CD4+ T-cell depletion in HIV disease. Nature
13. Moir S, Malaspina A, Pickeral OK, et al. Decreased survival of B cells of HIV-viremic patients mediated by altered expression of receptors of the TNF superfamily. J Exp Med
14. Kroon FP, Rimmelzwaan GF, Roos MT, et al. Restored humoral immune response to influenza vaccination in HIV-infected adults treated with highly active antiretroviral therapy. AIDS
15. Viard JP, Mocroft A, Chiesi A, et al. Influence of age on CD4 cell recovery in human immunodeficiency virus-infected patients receiving highly active antiretroviral therapy: evidence from the EuroSIDA study. J Infect Dis
16. Mackall CL, Fleisher TA, Brown MR, et al. Age, thymopoiesis, and CD4+ T-lymphocyte regeneration after intensive chemotherapy. N Engl J Med
17. Finkel DG, John G, Holland B, et al. Women have a greater immunological response to effective virological HIV-1 therapy. AIDS
18. Kaufmann GR, Perrin L, Pantaleo G, et al. CD4 T-lymphocyte recovery in individuals with advanced HIV-1 infection receiving potent antiretroviral therapy for 4 years: the Swiss HIV Cohort Study. Arch Intern Med
19. Hunt PW, Deeks SG, Rodriguez B, et al. Continued CD4 cell count increases in HIV-infected adults experiencing 4 years of viral suppression on antiretroviral therapy. AIDS
20. Maini MK, Gilson RJ, Chavda N, et al. Reference ranges and sources of variability of CD4 counts in HIV-seronegative women and men. Genitourin Med
21. Palella FJ Jr, Delaney KM, Moorman AC, et al. Declining morbidity and mortality among patients with advanced human immunodeficiency virus infection. HIV Outpatient Study Investigators. N Engl J Med
22. Hunt PW, Martin JN, Sinclair E, et al. T-cell activation is associated with lower CD4+ T-cell gains in human immunodeficiency virus-infected patients with sustained viral suppression during antiretroviral therapy. J Infect Dis
23. Kalayjian RC, Landay A, Pollard RB, et al. Age-related immune dysfunction in health and in human immunodeficiency virus (HIV) disease: association of age and HIV infection with naive CD8+ cell depletion, reduced expression of CD28 on CD8+ cells, and reduced thymic volumes. J Infect Dis
Keywords:© 2006 Lippincott Williams & Wilkins, Inc.
HIV-1; antiretroviral therapy; immunologic outcomes; CD4 cell recovery; T-cell activation; memory and naive CD4 cell subsets