Induction of prolonged survival of CD4+ T lymphocytes by intermittent IL-2 therapy in HIV-infected patients

Abstract

HIV infection leads to decreases in the number of CD4 T lymphocytes and an increased risk for opportunistic infections and neoplasms. The administration of intermittent cycles of IL-2 to HIV-infected patients can lead to profound increases (often greater than 100%) in CD4 cell number and percentage. Using in vivo labeling with 2H-glucose and BrdU, we have been able to demonstrate that, although therapy with IL-2 leads to high levels of proliferation of CD4 as well as CD8 lymphocytes, it is a remarkable preferential increase in survival of CD4 cells (with half-lives that can exceed 3 years) that is critical to the sustained expansion of these cells. This increased survival was time-dependent: the median half-life, as determined by semiempirical modeling, of labeled CD4 cells in 6 patients increased from 1.7 weeks following an early IL-2 cycle to 28.7 weeks following a later cycle, while CD8 cells showed no change in the median half-life. Examination of lymphocyte subsets demonstrated that phenotypically naive (CD27+CD45RO-) as well as central memory (CD27+CD45RO+) CD4 cells were preferentially expanded, suggesting that IL-2 can help maintain cells important for host defense against new antigens as well as for long-term memory to opportunistic pathogens.

Figure 1

CD4 and CD8 counts over time for 4 responders to intermittent IL-2 therapy who also participated in labeling studies. The blue lines indicate CD4 cell counts and the red lines indicate CD8 cell counts. The black lines indicate the baseline CD4 counts (mean of 3 values) immediately before the start of IL-2 therapy. Triangles represent individual 5-day IL-2 cycles (3 million to 18 million IU/d). Arrows indicate the IL-2 cycle during which labeling with ²H-glucose (²H) or BrdU was performed.

Figure 2

Deuterium incorporation by CD4 and CD8 cells. (A) Mean peak deuterium incorporation was significantly higher in HIV-infected patients receiving IL-2 (n = 18) for both CD4 and CD8 cell populations when compared with HIV-uninfected controls (n = 8) and HIV-infected patients who did not receive IL-2 (n = 9) (P < 0.001 for all comparisons, Student’s t test). Error bars represent the standard deviation. (B and C) Deuterium labeling kinetics in 2 HIV-infected patients who did not receive IL-2 (patients 20 and 22, Table 1) and an HIV^– volunteer (patient 30) (B) and in 3 HIV-infected patients who were long-term participants in intermittent IL-2 studies (patients 1, 2, and 4) (C). Patients 1 and 2 were long-term responders (see Figure 1 and Table 1), while patient 4 did not exhibit a CD4 count increase during IL-2 therapy. The continuous lines represent the fitting of the experimental data points (individual symbols) by the model equations. For the first 2 patients, the open symbol represents the percentage deuterium incorporation in cells obtained from a lymph node biopsy (at approximately 3 months). Time 0 is the beginning of the ²H-glucose infusion, which started 2 days after initiation of IL-2 treatment. (D) The probability density function (PD) of the normal distribution of log d multiplied by the total source of labeled cells (S) for the patients in C. The mean log decay rate constants (m_d) for CD4/CD8 cells for the patients are, respectively: patient (pt.) 1, –2.68/–1.68; pt. 2, –2.44/–1.44; pt. 4, 1.16/0.52. One log difference represents a 10-fold difference in half-life.

Figure 3

Slower decay of deuterium labeling in CD4 but not CD8 cells after later cycles of IL-2. (A and C) Mean log decay shifted to the left for CD4 cells (A) but not CD8 cells (C) in 5 of 6 patients, indicating a longer average survival of CD4 cells (but not CD8 cells) following later IL-2 cycles (3 to 6) compared to earlier cycles (1 to 3). Patient 3 had an infusion of ²H-glucose before beginning IL-2 therapy (green diamonds), and patient 5 received a third infusion during his fourth IL-2 cycle (purple circles). The solid lines represent the fitting by the model equations. (B and D) The probability density function of the normal distribution of log d multiplied by the total source of labeled cells (S). Mean log decay rate constants for CD4/CD8 cells for the patients are, respectively: pt. 3, –0.59/0.06 (no IL-2), –0.33/–0.91 (cycle 1), –1.79/–0.68 (cycle 6); pt. 5, –1.03/–0.95 (cycle 1), –1.80/–1.30 (cycle 3), –1.86/–1.39 (cycle 4); pt. 6, –0.09/–2.05 (cycle 2), –1.73/–2.19 (cycle 4); pt. 7, –0.45/–1.01 (cycle 2), –0.94/–1.07 (cycle 5); pt. 8, –1.07/–2.18 (cycle 3), –2.30/–2.20 (cycle 4); pt. 10, –1.14/–0.95 (cycle 1), –0.66/–0.92 (cycle 3).

Figure 4

BrdU labeling kinetics in 4 patients receiving a BrdU infusion immediately after the last IL-2 dose. (A) Experimental data for CD4 cells, represented by blue squares, and for CD8 cells, represented by red triangles. For patient 3 (top panels), data following labeling before any IL-2 was received are shown by green squares (CD4) and black triangles (CD8). The solid lines represent the fitting by the model equations. (B) The probability density function of the normal distribution of log d multiplied by the total source of labeled cells (S) for the same patients. The last 2 patients were long-term responders (patients 1 and 19 from Figure 1). Mean log decay m_d values for these data are (CD4/CD8): pt. 3, 0.10/–0.07 (for labeling with no IL-2), 0.14/0.88 (cycle 1); pt. 8, 1.38/0.85; pt. 1, –1.34/0.11; pt. 19, –1.28/0.35. Consistent with the deuterium-labeling studies, the 2 long-term responders had a smaller m_d for labeled CD4 but not CD8 cells, indicating longer survival of the proliferating cells. (C) BrdU labeling kinetics in naive (CD27⁺CD45RO^–), central memory (CD27⁺CD45RO⁺), and effector memory (CD27^–CD45RO⁺ and CD27^–CD45RO^–) CD4 (top) and CD8 (bottom) subpopulations for patient 19. Presentation of data is as in A and B. For both CD4 and CD8 cells, m_d is substantially smaller (indicating a slower decay) for the 2 CD27⁺ populations. Mean log decay m_d values for these data are (CD45RO^–/CD45RO⁺): CD4/CD27⁺, –1.58/–1.10; CD8/CD27⁺, –1.02/–1.32; CD4/CD27^–, 0.69/2.32; CD8/CD27^–, 0.07/1.92.

Figure 5

Deuterium labeling kinetics in naive (CD27⁺CD45RO^–) cells in patients receiving IL-2. The left panels show the measured data (symbols) and the fitting by the model equations (solid lines) for patients 3, 5, and 6 following an early cycle (blue) and a later cycle (red), and for patients 1 and 2 following the single late IL-2 cycle; the right panels show the probability density function of the normal distribution of log d multiplied by the total source of labeled cells (S). Mean log decay m_d values for these data are (early/late): –1.16/–2.52, –1.35/–2.61, and –1.49/–2.14 for patients 3, 5, and 6, respectively (P = 0.039 for early vs. late, Student’s t test), and –2.72 and –3.52 for patients 1 and 2, respectively. No significant change was seen in the mean log decay m_d for the other CD4 subsets or for any of the CD8 subsets for patients 3, 5, and 6. Average values for mean log decay m_d for these subsets were as follows (early/late): CD4 central memory (CD27⁺CD45RO⁺), –0.54/–0.70; CD4 effector memory (CD27^–CD45RO⁺), –0.59/–0.74; CD8 naive (CD27⁺CD45RO^–), –1.00/–1.90; CD8 central memory (CD27⁺CD45RO⁺), –0.82/–1.26; CD8 effector memory (CD27^–CD45RO⁺), –0.19/–0.36; CD8 effector memory (CD27^–CD45RO^–), –1.02/–1.13.