Ligand-Blocking and Membrane-Proximal Domain Targeting Anti-OX40 Antibodies Mediate Potent T Cell-Stimulatory and Anti-Tumor Activity.

Agonistic antibodies targeting the tumor necrosis factor (TNF) superfamily of co-stimulatory receptors (TNFRSF) are progressing through various stages of clinical development for cancer treatment, but the desired and defining features of these agents for optimal biological activity remain controversial. One idea, based on recent studies with CD40, is that non-ligand-blocking antibodies targeting membrane-distal cysteine-rich domain 1 (CRD1) have superior agonistic activities compared with ligand-blocking antibodies targeting more membrane-proximal CRDs. Here, we determined the binding and functional characteristics of a panel of antibodies targeting CRDs 1-4 of OX40 (also known as TNFRSF4 or CD134). In striking contrast to CD40, we found that ligand-blocking CRD2-binding and membrane-proximal CRD4-binding anti-OX40 antibodies have the strongest agonistic and anti-tumor activities. These findings have important translational implications and further highlight that the relationship between epitope specificity and agonistic activity will be an important issue to resolve on a case-by-case basis when optimizing antibodies targeting different co-stimulatory tumor necrosis factor receptors (TNFRs).

Determinants of Human CD134 Essential for Entry of Human Herpesvirus 6B.

We identified two key amino acid residues within human CD134 (hCD134) that are required for its interaction with human herpesvirus 6B (HHV-6B) and for HHV-6B entry into cells. One of the residues (K79) allows access of the HHV-6B ligand to hCD134. Murine CD134 (mCD134) functioned as an HHV-6B receptor when these two amino acid residues were replaced with homologous human residues. This study identifies both the HHV-6B receptor-ligand interaction and the species-specific determinants of hCD134 essential for HHV-6B entry.

Emergence of CD134 cysteine-rich domain 2 (CRD2)-independent strains of feline immunodeficiency virus (FIV) is associated with disease progression in naturally infected cats.

BACKGROUND: Feline immunodeficiency virus (FIV) infection is mediated by sequential interactions with CD134 and CXCR4. Field strains of virus vary in their dependence on cysteine-rich domain 2 (CRD2) of CD134 for infection. FINDINGS: Here, we analyse the receptor usage of viral variants in the blood of 39 naturally infected cats, revealing that CRD2-dependent viral variants dominate in early infection, evolving towards CRD2-independence with disease progression. CONCLUSIONS: These findings are consistent with a shift in CRD2 of CD134 usage with disease progression.

Detailed study of the interaction between human herpesvirus 6B glycoprotein complex and its cellular receptor, human CD134.

UNLABELLED: Recently, we identified a novel receptor, CD134, which interacts with the human herpesvirus 6B (HHV-6B) glycoprotein (g)H/gL/gQ1/gQ2 complex and plays a key role in the entry of HHV-6B into target cells. However, details of the interaction between the HHV-6B gH/gL/gQ1/gQ2 complex and CD134 were unknown. In this study, we identified a cysteine-rich domain (CRD), CDR2, of CD134 that is critical for binding to the HHV-6B glycoprotein complex and HHV-6B infection. Furthermore, we found that the expression of HHV-6B gQ1 and gQ2 subunits was sufficient for CD134 binding, which is different from the binding of human herpesvirus 6A (HHV-6A) to its receptor, CD46. Finally, we identified a region in gQ1 critical for HHV-6B gQ1 function. These results contribute much to our understanding of the interaction between this ligand and receptor. IMPORTANCE: We identified the domain in HHV-6B entry receptor CD134 and the components in the HHV-6B gH/gL/gQ1/gQ2 complex required for ligand-receptor binding during HHV-6B infection. Furthermore, we identified domains in gQ1 proteins of HHV-6A and -6B and a key amino acid residue in HHV-6B gQ1 required for its function. These data should be the basis for further investigation of ligand-receptor interaction in the study of HHV-6A and -6B.

Inherited human OX40 deficiency underlying classic Kaposi sarcoma of childhood.

Kaposi sarcoma (KS), a human herpes virus 8 (HHV-8; also called KSHV)-induced endothelial tumor, develops only in a small fraction of individuals infected with HHV-8. We hypothesized that inborn errors of immunity to HHV-8 might underlie the exceedingly rare development of classic KS in childhood. We report here autosomal recessive OX40 deficiency in an otherwise healthy adult with childhood-onset classic KS. OX40 is a co-stimulatory receptor expressed on activated T cells. Its ligand, OX40L, is expressed on various cell types, including endothelial cells. We found OX40L was abundantly expressed in KS lesions. The mutant OX40 protein was poorly expressed on the cell surface and failed to bind OX40L, resulting in complete functional OX40 deficiency. The patient had a low proportion of effector memory CD4(+) T cells in the peripheral blood, consistent with impaired CD4(+) T cell responses to recall antigens in vitro. The proportion of effector memory CD8(+) T cells was less diminished. The proportion of circulating memory B cells was low, but the antibody response in vivo was intact, including the response to a vaccine boost. Together, these findings suggest that human OX40 is necessary for robust CD4(+) T cell memory and confers apparently selective protective immunity against HHV-8 infection in endothelial cells.

Bivalent aptamers deliver the punch.

Aptamers, sometimes termed "chemical antibodies," have been engineered into multimerized versions for therapeutic application. The groups of Gilboa and Sullenger now report the development of a bivalent aptamer-molecular device as a receptor agonist that has the same functional properties, but stronger avidity than a corresponding antibody.

Assembling OX40 aptamers on a molecular scaffold to create a receptor-activating aptamer.

We show that a molecular scaffold can be utilized to convert a receptor binding aptamer into a receptor agonist. Many receptors (including tumor necrosis receptor family members) are activated when they are multimerized on the cell surface. Molecular scaffolds have been utilized to assemble multiple receptor binding peptide ligands to generate activators of such receptors. We demonstrate that an RNA aptamer that recognizes OX40, a member of the tumor necrosis factor receptor superfamily, can be converted into a receptor-activating aptamer by assembling two copies on an olignucleotide-based scaffold. The OX40 receptor-activating aptamer is able to induce nuclear localization of nuclear factor-kappaB, cytokine production, and cell proliferation, as well as enhance the potency of dendritic cell-based tumor vaccines when systemically delivered to mice.