Differential reconstitution of zidovudine-induced inhibition of mitogenic responses by interleukin-2 in peripheral blood mononuclear cells from patients with human immunodeficiency virus infection

Zidovudine (ZDV), an anti-human immunodeficiency virus (HIV) therapy, has been associated with reduction in mortality and improvement of patients with acquired immunodeficiency syndrome (AIDS). The ZDV recipients, however, experience a multitude of side effects of which bone marrow suppression is the most noteworthy, especially among patients with low CD4 cell counts. The effect of ZDV and interleukin-2 (IL-2) on phytohemagglutinin (PHA)-induced proliferative response of peripheral blood mononuclear cells (PBMs) from patients with HIV infection was investigated. ZDV 0.5 μg inhibited 40% of PHA-induced thymidine uptake in PBMs from healthy donors or patients with HIV, irrespective of their CD4 cell counts. However, IL-2 (10 U/ml) had differential effect on PHA-induced thymidine uptake that appeared to be dependent on absolute CD4 cell counts. While PBMs from patients with CD4 cell counts of 400/mm³ or more did not respond to IL-2 (low responders), IL-2 enhanced the PHA-induced thymidine uptake in PBMs from patients with CD4 cell counts less than 400/mm³ at an average of 60% (high responders). Moreover, IL-2 restored the ZDV-induced inhibition by almost 100% in the high responder group while it did not affect counts in the low responder group. The production of IL-2 in vitro, in response to PHA or recall antigens, was equivalently inhibited in both groups. These data suggest that ZDV and IL-2 could have an additive effect on immune parameters in certain groups of patients infected with HIV. The differential effect of IL-2 was independent of IL-2 receptor expression.