Eliciting VRC01-class antibodies against HIV-1 through immunization

Abstract

With more that 37 million people currently infected with HIV-1, there is a need for a vaccine to prevent HIV-1 infection. One goal of an effective HIV-1 vaccine is to elicit broadly neutralizing antibodies (bnAbs). These antibodies (Abs) neutralize the majority of HIV-1 viruses in circulation. bnAbs have been isolated from chronically infected individuals and were shown, in studies of passive administration in non-human primates and humanized mice, to be protective against SHIV and HIV respectively. Thus, it is thought that if bnAbs can be elicited through vaccination, they will be protective.VRC01-class Abs are amongst the most broad and potent neutralizing and therefore desirable to elicit during vaccination. VRC01-class Abs target the CD4-binding site (CD4-BS) on the HIV-1 Env. All members of this class have high levels of somatic hypermutation (SHM); share similar gene ontogenies, all utilizing the VH1-2*02 allele in the heavy chain paired with one of the following light chains: k3-20, k1-33, l2-14, k3-15, k1-5; and use the same mode of recognition to engage the CD4-BS. A major roadblock to eliciting such Abs is the fact that the unmutated or germline precursors which gives rise to these bnAbs fail to bind known recombinant Env. This has led to the development of immunogens that engage the germline (gl)VRC01 precursor, thus named germline-targeting immunogens. This thesis examines germline-targeting immunogens in vivo. The germline-targeting immunogens evaluated are Env-based and also anti-idiotypic antibodies (aiAbs). In Chapter II we evaluated Env-based germline-targeting immunogens. In these studies, we utilized a mouse model expressing B cells with the glVRC01 heavy chain (glH-VRC01 mouse, Table 1.3). Mice were immunized with one of the following germline-targeting immunogens: 426c Core, eOD- GT8, or 426cOD. These immunogens differ in their affinity for glVRC01, the structural presentation of the glVRC01 epitope, and genetically. We found that while all of the glVRC01- targeting immunogens effectively activated VRC01-like B cells in vivo, the immunogens selected for B cells with distinct genetic characteristics that influence their ability to recognize diverse Env proteins. These results will inform HIV-1 vaccine design, as both 426c Core and eOD-GT8 are being evaluated in human clinical trials. These results are also more broadly applicable to vaccine design, by highlighting the importance of structure and biophysical and biochemical properties of the immunogen on B cell activation. While, these germline-targeting immunogens are able to activate VRC01-like B cells in vivo, the Abs they produce are non-neutralizing. Therefore in the work reported in Chapter III, we employed a boosting immunogen in an effort to guide the maturation of these B cells to their neutralizing form. We found that priming glH-VRC01 mice with the germline-targeting immunogen 426c Core and boosting with the HxB2 wild type (WT) Core protein increased SHM in the VRC01-like B cell receptors, improved Ab binding to diverse Env proteins and increasedthe Abs ability to neutralize the autologous WT virus. This work is the first to identify a prime- boost immunization scheme that can elicit VRC01-class Abs capable of neutralizing a WT virus. We also evaluated the aiAb, iv8, as a glVRC01-class germline-targeting immunogen in Chapter IV. In an adoptive transfer experiment, we found that iv8 is able to activate and expand B cells expressing the mature 3BNC60 heavy chain and gl3BNC60 light chain (SI-3BNC60, Table 1.3), as well as decrease the non-VRC01-epitope targeted plasma Ab response in comparison to an Env-based immunogen. Iv8 was also able to expand B cells expressing VRC01-class characteristics in the glH-3BNC60 mouse model. Therefore, we have demonstrated that iv8 can activate glVRC01-class B cells in vivo and should be considered for use in combination or as an alternative to Env-based immunogens in vaccination studies designed to elicit VRC01-class bnAbs.