In our study, we examined the predictive value of the CCR5 genotype. The outcome of our analysis was that a wild-type CCR5 genotype increased the relative risk for progression of HIV disease with a factor of 2.5, independent of CD4⁺ T-lymphocyte counts, T-cell function, HIV-1 biological phenotype, and viral RNA load in serum. As we showed in a cumulative Kaplan-Meier analysis, persons with all markers in a beneficial mode had the longest survival; the persons with the most rapid progression had all markers in a bad mode.

Despite these, in our opinion, convincing data, Dr. Scribner claims that our remark that "The addition of CCR5 genotype to currently available laboratory markers may allow better estimation of the clinical course of HIV-1 infection" is not supported by the paper. Although Dr. Scribner appreciates the protective effect of CCR5 Delta32 heterozygosity in the clinical course of HIV-1 infection, he is disturbed because we have not made any claims about indications for use, clinical benefit, or even clinical importance. In support of his argument, Dr. Scribner mentions, correctly, that 50% of persons classified as long-term survivors in our case–control study had wild-type CCR5 genotype. However, the clinical course of HIV-1 infection is generally accepted to be determined by the interplay of multiple viral, immunologic, and host genetic factors; this is also supported by our cumulative Kaplan-Meier analysis, discussed above. We never intended to suggest that CCR5 genotyping by itself would provide sufficient information. Therefore, we chose the wording of our remark (cited above) carefully.

This, of course, is an academic point of view and does not consider cost–benefit aspects; this is far beyond our expertise. We did not intend to make a statement on whether CCR5 genotyping should be performed as a commercial test or whether it should be further analyzed in the research realm. Although we believe that a more accurate estimate of an HIV-infected person's clinical course and life expectancy would justify any laboratory measurement, we fully underscore the opinion of Dr. Scribner that a proper cost–benefit analysis for each test is essential to keep the costs of medical care within certain limits.