261-T.
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Protection in Vitro among HIV-Exposed Uninfected Individuals
R. John*, S. Arango-Jaramillo, and D. Schwartz
Johns Hopkins Univ., Baltimore, MD
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Background: Repeatedly HIV-exposed uninfected (EU) individuals resist infection through known and unknown mechanisms. Homozygous DELTAC32 mutation results in absent Sccr5, but is rare among Eus. Other factors causing low sCCR5, and preexisting alloimmunity have been implicated, but usually the basis of in vivo resistance is unknown and may be multifactorial. Initial relative resistance could allow immunizing exposures to progressively enhance initial resistance. Our published in vitro challenge of PBMCs from Eus, showing relative resistance to R5 BaL, is part of a conflicting literature, which may reflect the fact that in vivo resistance of Eus is incomplete. EU PBMCs contain both target and antiviral cells. The outcome of in vitro challenge depends on their relative susceptibility and antiviral activity. We hypothesized that, in the absence of DELTAC32: increasing R5 viral dose would cause breakthrough infections; in vitro resistance to challenge would partially cross clades, due to broadly shared epitopes and/or dependence on factors (e.g., chemokines) affecting CCR5.
Methods: Eus with high-risk behavior for > 2 years were recruited. In vitro protection was examined among 18 remaining seronegative over 2-4 years of follow-up. Quadruplicate cultures of cryopreserved PBMCs were stimulated with anti-CD3 + IL-2 for 4 days, and challenged with 3 & 50 TCID50 of a local 1o clade B isolate, and 5 TCID50 of a 1o clade C & E isolate. CD8-depleted PBMCs were challenged in parallel with clade B virus. beta-chemokines were measured by EIA in day of challenge supernatants.
Results: At 3 TCID50, virus infected 46/76 (60%) control cultures, but only 8/63 (13%) EU cultures (p<0.001). At 50 TCID50, p24 was detected in almost all cultures, but 6/11 Eus restricted p24 to < 10% of controls. CD8 cell depletion abrogated protection in 7/14 EU individuals, while beta-chemokine production was elevated in the EUs as a group vs controls (p<0.05 for RANTES and MIP-1beta). Challenge with 5 TCID50 clade C or E HIV gave 28/34 (82%) and 54/72 (75%) positive control wells, vs14/31(45%) and 35/63 (56%), respectively, in EU PBMCs (p<0.01, for both clade C and E).
Conclusions: EUs can have multiple protective mechanisms with cross clade activity, suggesting vaccines will work against low-dose exposures to multiple clades.
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