The reason doctors would use O neg blood derived Rhogam products to treat HIV positive patients is that 0 neg blood is the universal donor blood type. Any HIV/rh positive patient could accept O neg derived blood products, but no so for A-, B- or, AB-. It's a stretch to assume this automatically means O negatives are immune to HIV, and even if it is true, it does not mean only O negs have a genetic immunity to HIV. Any rh neg person could also carry one or two copies of the CCR5 Delta 32 gene. And so could some rh positive people. See, the CCR5 Delta 32 gene is not blood based, though it does seem there is a high percentage of rh negs among the Western European populations who carry the CCR5 Delta 32 gene.