All viruses sensitive to PG9 had a PNG at position 160 (black), whereas this was not the case for viruses resistant to PG9 (gray). PGT Antibodies Might Have an Even Stronger R5-Bias and Could Drive HIV Variants Toward Developing CXCR4-Usage PF-4136309 Capability It has been shown that this highly potent PGT-neutralizing antibodies interact with V3 sites 323, 324, 325, and 327 as well as N-linked glycans at position 301 and/or 332.17,18 Thus, these antibodies might also exhibit stronger neutralization capabilities against R5 viruses than against X4-capable viruses. panel of 199 diverse HIV-1 isolates, we found a statistically significant association between viral resistance to PG9 and PG16 and CXCR4 coreceptor usage (= 0.0011 and = 0.0010, respectively). Our analysis of viral variants from HIV-1Cinfected humanized mice under treatment with the broadly neutralizing antibody PGT128 indicated that certain antibodies might drive a viral populace toward developing CXCR4 coreceptor usage capability (= 0.0011 for the comparison between PGT128 and control measurement). Conclusions: These analyses spotlight the importance of accounting for any possible coreceptor usage bias pertaining to the effectiveness of an HIV vaccine and to passive antibody transfer as therapeutic approach. Key Words: broadly neutralizing antibodies, HIV, vaccine, coreceptor tropism INTRODUCTION With more than 2.5 million new HIV-1 infections each year, there is an urgent need for additional protective measures against this virus. A natural approach to preventing HIV infections would be to vaccinate people with a universal HIV vaccine. One alternate is to induce neutralizing antibodies that interfere with the process of viral cell access like for hepatitis B vaccine. Regrettably, because of the high genomic diversity of HIV, a universal HIV vaccine that elicits broad neutralization responses against most of the existing HIV strains has not yet been discovered.1 Most recent approaches to isolate PF-4136309 broadly neutralizing antibodies from patient sera2C4 have demonstrated promising results. One of these new antibodies, PG9, has been shown to interact with the glycan shield and specific sites of the variable loops 1 and 2 as well as the variable loop 3 (V3)2,5 of the protein of the virus. The structure of these loops largely determines which coreceptor the computer virus can use for entering and infecting new cells. The two coreceptors that are mainly relevant in vivo are the chemokine receptors CCR5 and CXCR4. Viruses that can only bind to the CCR5 coreceptor are called R5 viruses, and viruses that can only use the CXCR4 coreceptor are called X4 viruses. Generally, viruses capable of binding to both coreceptors are called dual-tropic viruses, however, the discrimination of dual-tropic and X4 viruses is difficult to make both by genotypic and (commercially available) phenotypic assays. Here, we refer to X4-capable viruses for both, X4 viruses and dual-tropic viruses. These have very low PF-4136309 capacity of newly infecting humansat least by sexual transmissionas evidenced by the highly significant underrepresentation of individuals with a homozygous 32 variant of the CCR5 structural gene among seropositive white individuals.6 These people lack a functional CCR5 coreceptor and therefore cannot be infected by R5 viruses. The fact that only very few individuals with this mutation were HIV seropositive as compared with the mutation frequency in the population indicates that R5 viruses might be more relevant regarding new infections than X4-capable viruses. Thus, a vaccine needs to elicit responses against R5 viruses, but responses against X4-capable viruses are less important for preventing HIV contamination. Beyond using knowledge about broadly neutralizing antibodies for vaccine design, it might be possible to effectively treat HIV-1Cinfected patients with a combination of these antibodies. Klein et PF-4136309 al7 showed that HIV-1Cinfected humanized mice could be effectively treated by a combination IKBKB antibody of broadly neutralizing antibodies and proposed to re-examine this approach as a treatment modality in HIV-1Cinfected patients. Recent studies in SHIV-infected Rhesus macaques also yielded encouraging results.8,9 In this work, we show that there is a significant association between CXCR4 coreceptor usage and resistance to PG9 and PG16.2 We provide evidence that this may have important implications both for vaccination methods and for therapeutic methods: The first implication is while configuring a panel assessing neutralization capacities of antibodies against HIV-1, one should take coreceptor usage of the strains into account for an unbiased evaluation of an antibody’s capacity to neutralize strains that can establish an infection. The second implication is that certain antibodies such as PGT128, which was one of the antibodies Klein et al7 used in their study, might drive the viral PF-4136309 populace toward developing CXCR4 coreceptor usage capability. This is supported by our analysis on data from their study showing a significant difference between coreceptor usage of the variants.