Mucosal integrin α4β7 blockade fails to reduce the seeding and size of viral reservoirs in SIV-infected rhesus macaques

Whole-body PET imaging of simian immunodeficiency virus using gp120-targeting probes fails to reveal regions of specific uptake in rhesus macaques

PURPOSE

Following the initial reports demonstrating the feasibility of immunoPET imaging of simian immunodeficiency virus (SIV) using gp120-targeting monoclonal antibodies in non-human primates, replication efforts of the imaging system in human immunodeficiency virus (HIV)-infected individuals have yielded conflicting results. Herein, we used two anti-gp120 antibodies, 7D3 and ITS103.01LS-F(ab')2, to interrogate the reproducibility of gp120-targeting probes for immunoPET imaging of SIV in rhesus macaques.

METHODS

The binding affinity estimates of 89Zr radiolabeled 7D3 and ITS103.01LS-F(ab')2 to SIV gp120, and the in-vitro and ex-vivo binding specificities of [89Zr]Zr-7D3 and [89Zr]Zr-ITS103.01LS-F(ab')2 to SIV Env expressing cells, primary cells, and tissue sections from uninfected and SIV-infected macaques were obtained through competition assays. The biodistributions of [89Zr]Zr-7D3 and [89Zr]Zr-ITS103.01LS-F(ab')2 were performed with static PET scans up to 6 days post-injection in 20 rhesus macaques and the standardized uptake values in various tissues were compared between SIV-infected and uninfected controls.

RESULTS

Despite the demonstrated nanomolar affinity of [89Zr]Zr-7D3 and [89Zr]Zr-ITS103.01LS-F(ab')2 to SIV gp120, and strong binding specificity to SIV gp120 cell lines, we observed no discernible differences in their binding in primary cells, tissue sections of secondary lymphoid organs, in-vivo probe uptake between SIV-infected and uninfected macaques, or ex-vivo validation necropsies. While the probes remained stable in-vivo, only [89Zr]Zr-ITS103.01LS-F(ab')2 in chronic plasma retained its binding specificity to SIV gp120, with [89Zr]Zr-7D3 experiencing a > 97% reduction in binding to gp120 due to competition from endogenous antibodies at the 7D3 binding site.

CONCLUSION

The overall absence of specific uptake suggests inadequate binding potential (ligand affinity x target molarity) for these probes to effectively image SIV or HIV in-vivo, warranting further investigation into the lack of reproducibility observed with earlier non-human primate SIV imaging and conflicting human studies.

Early treatment with anti-α4β7 antibody facilitates increased gut macrophage maturity in SIV-infected rhesus macaques

Despite advances in combination antiretroviral therapy (cART), people living with HIV (PLWH) continue to experience gastrointestinal dysfunction. Infusions of anti-α4β7 monoclonal antibodies (mAbs) have been proposed to increase virologic control during simian immunodeficiency virus (SIV) infection in macaques with mixed results. Recent evidences suggested that therapeutic efficacy of vedolizumab (a humanized anti-α4β7 mAb), during inflammatory bowel diseases depends on microbiome composition, myeloid cell differentiation, and macrophage phenotype. We tested this hypothesis in SIV-infected, anti-α4β7 mAb-treated macaques and provide flow cytometric and microscopic evidence that anti-α4β7 administered to SIV-infected macaques increases the maturity of macrophage phenotypes typically lost in the small intestines during SIV disease progression. Further, this increase in mature macrophage phenotype was associated with tissue viral loads. These phenotypes were also associated with dysbiosis markers in the gut previously identified as predictors of HIV replication and immune activation in PLWH. These findings provide a novel model of anti-α4β7 efficacy offering new avenues for targeting pathogenic mucosal immune response during HIV/SIV infection.

Host membrane proteins in the HIV-induced membrane fusion: Role in pathogenesis and therapeutic potential of autoantibodies

Host proteins such as receptors, adhesion and signaling molecules, promote virus-cell fusion, virus cell-cell transmission, and formation of multinucleated cells with outstanding properties. These events are implicated in virus dissemination and the induction of pathological effects such as the infection of the gut-associated lymphoid tissue, placenta infection, and neurological complications. Antibodies directed to the host membrane proteins are produced during the natural HIV infection and may contribute significantly to virus inhibition. Antibodies against the HIV receptor have been approved for therapy and others targeting additional host membrane proteins are currently under evaluation. This review emphasizes the relevance of the different pathways of HIV spreading between cells and of antibodies directed to host membrane components in the development of broad-range therapeutics against HIV.

Eliminating HIV reservoirs for a cure: the issue is in the tissue

PURPOSE OF REVIEW

Advances in antiretroviral therapy have saved numerous lives, converting a diagnosis with human immunodeficiency virus 1 (HIV-1) from a death sentence into the possibility for a (nearly) normal life in many instances. However, the obligation for lifelong adherence, increased risk of accumulated co-morbidities, and continued lack of uniform availability around the globe underscores the need for an HIV cure. Safe and scalable HIV cure strategies remain elusive, in large part due to the presence of viral reservoirs in which caches of infected cells remain hidden from immune elimination, primarily within tissues. Herein, we summarize some of the most exciting recent advances focused on understanding, quantifying, and ultimately targeting HIV tissue viral reservoirs.

RECENT FINDINGS

Current studies have underscored the differences between viral reservoirs in tissue compartments as compared to peripheral blood, in particular, the gastrointestinal (GI) tract. Additionally, several novel or modified techniques are showing promise in targeting the latent viral reservoir, including modifications in drug delivery platforms and techniques such as CRISPR.

SUMMARY

Elimination of tissue viral reservoirs is likely the key to generation of an effective HIV cure. Exciting studies have come out recently that reveal crucial insights into topics ranging from the basic biology of reservoir seeding to effective drug targeting. However, there are still many outstanding questions in the field about the relative importance of specific reservoirs, such as the GI tract, that may alter the final strategy pursued.

The Hitchhiker Guide to CD4+ T-Cell Depletion in Lentiviral Infection. A Critical Review of the Dynamics of the CD4+ T Cells in SIV and HIV Infection

CD4⁺ T-cell depletion is pathognomonic for AIDS in both HIV and simian immunodeficiency virus (SIV) infections. It occurs early, is massive at mucosal sites, and is not entirely reverted by antiretroviral therapy (ART), particularly if initiated when T-cell functions are compromised. HIV/SIV infect and kill activated CCR5-expressing memory and effector CD4⁺ T-cells from the intestinal lamina propria. Acute CD4⁺ T-cell depletion is substantial in progressive, nonprogressive and controlled infections. Clinical outcome is predicted by the mucosal CD4⁺ T-cell recovery during chronic infection, with no recovery occurring in rapid progressors, and partial, transient recovery, the degree of which depends on the virus control, in normal and long-term progressors. The nonprogressive infection of African nonhuman primate SIV hosts is characterized by partial mucosal CD4⁺ T-cell restoration, despite high viral replication. Complete, albeit very slow, recovery of mucosal CD4+ T-cells occurs in controllers. Early ART does not prevent acute mucosal CD4⁺ T-cell depletion, yet it greatly improves their restoration, sometimes to preinfection levels. Comparative studies of the different models of SIV infection support a critical role of immune activation/inflammation (IA/INFL), in addition to viral replication, in CD4⁺ T-cell depletion, with immune restoration occurring only when these parameters are kept at bay. CD4⁺ T-cell depletion is persistent, and the recovery is very slow, even when both the virus and IA/INFL are completely controlled. Nevertheless, partial mucosal CD4⁺ T-cell recovery is sufficient for a healthy life in natural hosts. Cell death and loss of CD4⁺ T-cell subsets critical for gut health contribute to mucosal inflammation and enteropathy, which weaken the mucosal barrier, leading to microbial translocation, a major driver of IA/INFL. In turn, IA/INFL trigger CD4⁺ T-cells to become either viral targets or apoptotic, fueling their loss. CD4⁺ T-cell depletion also drives opportunistic infections, cancers, and comorbidities. It is thus critical to preserve CD4⁺ T cells (through early ART) during HIV/SIV infection. Even in early-treated subjects, residual IA/INFL can persist, preventing/delaying CD4⁺ T-cell restoration. New therapeutic strategies limiting mucosal pathology, microbial translocation and IA/INFL, to improve CD4⁺ T-cell recovery and the overall HIV prognosis are needed, and SIV models are extensively used to this goal.