In particular, while H-2band H-2khaplotypes present poorly at I-A (the former due to being a generally poor MHC presenter (74), the latter selectively poor for the MPER), the H-2spresents/binds a THepitope at I-A with an affinity/certainty that is equal to the H-2dresponder strain (Table S1)
In particular, while H-2band H-2khaplotypes present poorly at I-A (the former due to being a generally poor MHC presenter (74), the latter selectively poor for the MPER), the H-2spresents/binds a THepitope at I-A with an affinity/certainty that is equal to the H-2dresponder strain (Table S1). to provide T-cell help. H-2drestricted MPER+serum Ab responses depended on CD4 THinteractions with Class II (as revealed in immunized intra-H-2d/bcongenic or CD154-/-H-2dstrains, and by selective abrogation of MPER re-stimulated, H-2d-restricted primed splenocytes by Class II-blocking Abs), and failed to neutralize HIV-1 in the TZM-b/l neutralization assay, coinciding with lack of specificity for an aspartate residue in the neutralization core PF-3758309 of BnAb 2F5. Unexpectedly, H-2drestricted MPER+responses functionally mapped to a core THepitope partially overlapping the 2F5/z13/4E10 BnAb epitopes as well as non-neutralizing B-cell/Ab binding residues. We propose that Class II-restriction contributes to the general heterogeneity of non- neutralizing gp41 responses induced by Env. Moreover, the proximity of THand B-cell epitopes in this restriction PF-3758309 may have to be considered in re-designing minimal MPER immunogens aimed at exclusively binding BnAb epitopes and triggering MPER+BnAbs. Abbreviations used:HIV-1, Env, MPER, BnAbs, 2F5, Immunogen == Introduction == An efficacious, protective HIV-1 vaccine will likely require the robust induction of Abs capable of neutralizing a wide array of HIV-1 isolatesi.e., broadly neutralizing antibodies (BnAbs) (1). This notion is usually corroborated by experiments demonstrating sterilizing protection either upon passive transfer of BnAbs at physiological levels, preceding SHIV challenge in non-human primate (2-4) or via their retroviral transduction in humanized mice, prior to HIV-1 contamination (5). Unfortunately, efforts to elicit relevant BnAb titers by vaccination have been unsuccessful. Furthermore, in chronically infected HIV-1 individuals, BnAbs arise in a minority of subjects, typically years after transmission, and/or only transiently (6,7). In contrast to these rare (subdominant) BnAb responses, robust (dominant) Ab responses to non-neutralizing envelope (Env) HIV-1 epitopes are induced early in HIV-1 contamination, followed by varying degrees of strain-specific or limited neutralizing Ab responses (6,8,9). Recently, efforts to develop vaccine strategies for inducing BnAbs have been re-invigorated by advances in high- throughput recombinant Ab technology, that has led to the isolation of many novel BnAbs from chronically-infected subjects, and defined new vulnerable Env epitopes for targeting by vaccines (10). One such vaccine target is the membrane proximal external region (MPER) of gp41, a conserved region made up of contiguous epitopes of several BnAbs, including 2F5, 4E10, Z13 and 10E8 (11-16). Explanations for the dearth of MPER-specific BnAbs have included limited BnAb epitope accessibility due to topological constraints in the MPER (17-22); reviewed in (23-25). We have recently exhibited the depletion, inactivation, and/or modification of MPER BnAb epitope+B-cells via immunological tolerance (26), based on two of the better-studied MPER+BnAbs, 2F5 and 4E10, exhibiting self-/polyreactivityin vitro(27). Supporting this latter hypothesis are several observations we have made in knockin mice expressing the original (somatically-mutated) 2F5 or 4E10 V(D)J and VJ rearrangements (2F5/4E10 VH VLKI mice): i) expression of these rearrangements results in profound deletion of BM B-cells expressing them as B-cell receptors (BCRs) (28,29), akin to other KI models expressing BCRs with high affinities for self-antigens (30-32) ii) residual 2F5/4E10 KI B-cells poorly express, and flux calcium through, their BCRs (28,29,33), thus resembling unresponsive (anergic) B-cells (34,35), iii) residual anergic B-cells from 2F5 KI mice can be re-awakened by a TLR agonist-MPER peptide-liposome conjugate immunogen to produce clinically-relevant serum BnAb titers PF-3758309 (36), suggesting immunogen RH-II/GuB conformation is not limiting to elicitation of pre-existing B-cells expressing BnAbs targeting the 2F5 neutralization epitope, and iv) KI mice expressing germline (unmutated) 2F5 H chains exhibit a developmental blockade at least as early and profound as those carrying the original 2F5 Ab (33,36), suggesting that B-cells in the human pre-immune repertoire express unmutated 2F5 BCRs would be subjected to comparable, early tolerance checkpoints. Although the above-mentioned results in PF-3758309 our 2F5 KI model support its physiological relevance to assess how anergic B-cells can be targeted via immunization, it does not address other potentially important contributory factors limiting BnAb induction in normal, outbred animals or in healthy individualsi.e., with polyclonal germline (unmutated) pre-immune repertoires. In this context, vaccination in rhesus macaques, using the same regimen that breaks anergy and triggers robust BnAb responses in 2F5 complete KI mice, induces Abs focused to 2F5’s core neutralization epitope DKW (14) but fails to elicit BnAb responses (37) at least partly because vaccine-elicited Abs PF-3758309 lack somatic mutations required to either bind lipids (38,39) or alter.