Increased T-cell colony formation in AIDS patients treated with zidovudine: A possible mechanism for increased lymphocyte number

Treatment of AIDS patients with zidovudine is associated with an increase in lymphocyte counts. The mechanism for this increase is unclear and somewhat surprising in view of the myelosuppressive effect of zidovudine. To investigate this further, we measured lym-phocyte numbers, T-cell subsets, and the ability of peripheral blood mononuclear cells (PBMC) to form T-cell colonies (T-CFC) in agar formation, in a group of patients with AIDS, before and during the first 6 months of zidovudine treatment. Eight patients were treated for an average of 11 weeks. There was a significant increase in T-CFC with zi-dovudine treatment (11.5 ± 4.7% versus 29.8 ± 6.9%, P < 0.02 using a paired Student's t-test). There was a non-significant trend in the improvement of lymphocyte counts in these patients (872 ± 117 versus 1102 ± 204, NS). In vitro exposure of lymphocytes to zidovudine (200Limol/l) resulted in modest suppression of T-CFC formation, suggesting that the effect of zidovudine treatment is indirect. Given that we have previously shown that inactivated HIV can inhibit T-CFC formation, we suggest that zidovudine treatment indirectly allows an increase in lymphocyte number by decreasing virus load, thereby permitting greater T-cell repopulation.