Background:  Flow cytometry allows detailed evaluation of the immunologic condition of HIV patients, enumerating proportions of naive, memory, and activated cells among others. We investigated the relationships among changes in 10 lymphocyte subpopulations, total CD4, and HIV RNA in 138 children with advanced HIV disease enrolled in Pediatric AIDS Clinical Trials Group (PACTG) 366, hypothesizing that distinct interactions among T-cell subpopulations would be associated with distinct immune reconstitution and HIV RNA control.  

Methods:   We assembled 3-color flow data on 138 children aged 6 months to 17 years at entry in PACTG 366, a prospective, partially randomized, open-label trial of novel HAART regimens. All patients received 4 ART drugs with at least 1 protease inhibitor (PI) and 1 non-nucleoside reverse transcriptase inhibitor (NNRTI), with as long as 2 years’ follow-up. The 10 subsets defined by 3-color flow were naive, activated HLA-DR⁺CD38⁺, activated HLA-DR⁺, activated CD38⁺, and activated Fas⁺, for CD4 and CD8 subsets. Percentage of cells in each subset was transformed to an age-corrected z-score using quantiles published from PACTG P1009.

Results:  The baseline, 10-component vector of 3-color flow z-scores was combined with baseline total CD4 and HIV RNA to create an immunologic-virologic signature. The k-means clustering procedure was applied to identify 3 basic classes of signature:  common (n = 77, all components have median z-scores <2 in absolute value), activated (n = 47, median z-scores for activated, and activated HLA-DR⁺ CD4 and CD8 range from 3.4 to 5.0), and highly activated CD4 (n = 14, minimum of activated and activated HLA-DR⁺ CD4 z-scores >10). Baseline signature was strongly predictive of 24-week HIV RNA change, with individuals in the common signature reducing average RNA load by 1.4 (log₁₀) relative to highly activated CD4 signature reducing HIV RNA by only 0.5 (log₁₀, p = 0.007). CD4 reconstitution and maintenance over 24 weeks was also strongly associated with baseline signature, with the common signature achieving mean P1009 z = –1.28, but the activated signature achieving z = –4.1 (p <0.0001). Both findings are monotone in quantity of activation (ie, common > activated > highly activated) and all inferences are preserved after controlling for treatment received. 

Conclusions:  In advanced pediatric HIV disease, elevated markers of CD4 subset activation appear to strongly signal a poorer clinical course.