Relative preservation of natural killer cell cytotoxicity and number in healthy AIDS patients with low CD4 cell counts

Objective: This study examines whether there may be an immune component that protects a relatively rare group of HIV-infected people with very low CD4 cell counts (≤ 50 × 10⁶/l) who have prolonged asymptomatic periods. Design/methods: Three groups were recruited in Miami: (i) healthy low CD4 cell count patients (HLC; n = 30) who, for 9 months had < 50 × 10⁶ CD4 cells/l, were asymptomatic and were not on protease inhibitors during that time; (ii) HIV comparison group (Comp; n = 60) who had CD4 cell counts predominantly 150 × 10⁶ to 400 × 10⁶/l and never had AIDS Category C symptoms; this group was also followed for CD4 cell count and viral load change over 6 months; and (iii) healthy community controls (n = 33). The study was replicated at the University of California at Los Angeles (UCLA) with HLC (n = 31) versus HIV-negative laboratory controls (n = 28). Results: The HLC patients were significantly higher than the Comp group on natural killer cell cytotoxicity (NKCC) and natural killer cell number (NK#) despite their lower CD4 cell numbers and higher viral loads. In fact, there was no difference between the HLC group and the healthy community control group in NK# or NKCC. The NK findings were replicated at UCLA. A retrospective analysis showing that higher NKCC was related to fewer prior symptoms in the HLC group, and prospective analysis in the Comp group showing that NK# predicted a lower increase in viral load over 6 months further supported the importance of NK# and NKCC. Conclusions: Non-specific cellular immunity may be a factor protecting the health of HIV sero-positive individuals with very low CD4 cell counts.