BYON4228 is a pan-allelic antagonistic SIRPα antibody that potentiates destruction of antibody-opsonized tumor cells and lacks binding to SIRPγ on T cells.

BACKGROUND: Preclinical studies have firmly established the CD47-signal-regulatory protein (SIRP)α axis as a myeloid immune checkpoint in cancer, and this is corroborated by available evidence from the first clinical studies with CD47 blockers. However, CD47 is ubiquitously expressed and mediates functional interactions with other ligands as well, and therefore targeting of the primarily myeloid cell-restricted inhibitory immunoreceptor SIRPα may represent a better strategy. METHOD: We generated BYON4228, a novel SIRPα-directed antibody. An extensive preclinical characterization was performed, including direct comparisons to previously reported anti-SIRPα antibodies. RESULTS: BYON4228 is an antibody directed against SIRPα that recognizes both allelic variants of SIRPα in the human population, thereby maximizing its potential clinical applicability. Notably, BYON4228 does not recognize the closely related T-cell expressed SIRPγ that mediates interactions with CD47 as well, which are known to be instrumental in T-cell extravasation and activation. BYON4228 binds to the N-terminal Ig-like domain of SIRPα and its epitope largely overlaps with the CD47-binding site. BYON4228 blocks binding of CD47 to SIRPα and inhibits signaling through the CD47-SIRPα axis. Functional studies show that BYON4228 potentiates macrophage-mediated and neutrophil-mediated killing of hematologic and solid cancer cells in vitro in the presence of a variety of tumor-targeting antibodies, including trastuzumab, rituximab, daratumumab and cetuximab. The silenced Fc region of BYON4228 precludes immune cell-mediated elimination of SIRPα-positive myeloid cells, implying anticipated preservation of myeloid immune effector cells in patients. The unique profile of BYON4228 clearly distinguishes it from previously reported antibodies representative of agents in clinical development, which either lack recognition of one of the two SIRPα polymorphic variants (HEFLB), or cross-react with SIRPγ and inhibit CD47-SIRPγ interactions (SIRPAB-11-K322A, 1H9), and/or have functional Fc regions thereby displaying myeloid cell depletion activity (SIRPAB-11-K322A). In vivo, BYON4228 increases the antitumor activity of rituximab in a B-cell Raji xenograft model in human SIRPαBIT transgenic mice. Finally, BYON4228 shows a favorable safety profile in cynomolgus monkeys. CONCLUSIONS: Collectively, this defines BYON4228 as a preclinically highly differentiating pan-allelic SIRPα antibody without T-cell SIRPγ recognition that promotes the destruction of antibody-opsonized cancer cells. Clinical studies are planned to start in 2023.

Polyadenylation of genomic RNA and initiation of antigenomic RNA in a positive-strand RNA virus are controlled by the same cis-element.

Genomes and antigenomes of many positive-strand RNA viruses contain 3'-poly(A) and 5'-poly(U) tracts, respectively, serving as mutual templates. Mechanism(s) controlling the length of these homopolymeric stretches are not well understood. Here, we show that in coxsackievirus B3 (CVB3) and three other enteroviruses the poly(A) tract is approximately 80-90 and the poly(U) tract is approximately 20 nt-long. Mutagenesis analysis indicate that the length of the CVB3 3'-poly(A) is determined by the oriR, a cis-element in the 3'-noncoding region of viral RNA. In contrast, while mutations of the oriR inhibit initiation of (-) RNA synthesis, they do not affect the 5'-poly(U) length. Poly(A)-lacking genomes are able to acquire genetically unstable AU-rich poly(A)-terminated 3'-tails, which may be generated by a mechanism distinct from the cognate viral RNA polyadenylation. The aberrant tails ensure only inefficient replication. The possibility of RNA replication independent of oriR and poly(A) demonstrate that highly debilitated viruses are able to survive by utilizing 'emergence', perhaps atavistic, mechanisms.

Structural and functional integrity of the coxsackievirus B3 oriR: spacing between coaxial RNA helices.

The enterovirus oriR is composed of two helices, X and Y, anchored by a kissing (K) interaction. For proper oriR function, certain areas of these helices should be specifically oriented towards each other. It was hypothesized that the single-stranded nucleotides bridging the coaxial helices (Y-X and K-Y linkers) are important to determine this orientation. Spatial changes were introduced by altering the linker length between the helices of the coxsackievirus B3 oriR. Changing the linker lengths resulted in defective RNA replication, probably because of an altered oriR geometry. The identity of the linker residues also played a role, possibly because of sequence-specific ligand recognition. Although each point mutation altering the primary sequence of the Y-X spacer resulted in defective growth at 36 degrees C, the mutations had a wild-type phenotype at 39 degrees C, indicating a cold-sensitive phenotype. The results show that the intrinsic connection between oriR structure and function is fine-tuned by the spacing between the coaxial RNA helices.

Mutational analysis of different regions in the coxsackievirus 2B protein: requirements for homo-multimerization, membrane permeabilization, subcellular localization, and virus replication.

The coxsackievirus 2B protein is a small hydrophobic protein (99 amino acids) that increases host cell membrane permeability, possibly by forming homo-multimers that build membrane-integral pores. Previously, we defined the functional role of the two hydrophobic regions HR1 and HR2. Here, we investigated the importance of regions outside HR1 and HR2 for multimerization, increasing membrane permeability, subcellular localization, and virus replication through analysis of linker insertion and substitution mutants. From these studies, the following conclusions could be drawn. (i) The hydrophilic region ((58)RNHDD(62)) between HR1 and HR2 is critical for multimerization and increasing membrane permeability. Substitution analysis of Asn(61) and Asn(62) demonstrated the preference for short polar side chains (Asp, Asn), residues that are often present in turns, over long polar side chains (Glu, Gln). This finding supports the idea that the hydrophilic region is involved in pore formation by facilitating a turn between HR1 and HR2 to reverse chain direction. (ii) Studies undertaken to define the downstream boundary of HR2 demonstrated that the aromatic residues Trp(80) and Trp(82), but not the positively charged residues Arg(81), Lys(84), and Lys(86) are important for increasing membrane permeability. (iii) The N terminus is not required for multimerization but does contribute to the membrane-active character of 2B. (iv) The subcellular localization of 2B does not rely on regions outside HR1 and HR2 and does not require multimerization. (v) Virus replication requires both the membrane-active character and an additional function of 2B that is not connected to this activity.

Biological significance of a human enterovirus B-specific RNA element in the 3' nontranslated region.

The secondary structures predicted for the enteroviral 3' nontranslated region (3'NTR) all seem to indicate a conformation consisting of two (X and Y) hairpin structures. The higher-order RNA structure of the 3'NTR appears to exist as an intramolecular kissing interaction between the loops of these two hairpin structures. The enterovirus B-like subgroup possesses an additional stem-loop structure, domain Z, which is not present in the poliovirus-like enteroviruses. It has been suggested that the Z domain originated from a burst of short sequence repetitions (E. V. Pilipenko, S. V. Maslova, A. N. Sinyakov, and V. I. Agol, Nucleic Acids Res. 20:1739-1745, 1992). However, no functional features have yet been ascribed to this enterovirus B-like-specific RNA element in the 3'NTR. In this study, we tested the functional characteristics and biological significance of domain Z. A mutant of the cardiovirulent coxsackievirus group B3 strain Nancy which completely lacked the Z domain and which therefore acquired enterovirus C-like secondary structures exhibited a wild-type growth phenotype, as determined by single-cycle growth analysis with BGM cells. This result proves that the Z domain is virtually dispensable for viral growth in tissue cultures. Partial distortion of the Z domain structure resulted in a disabled virus with reduced growth kinetics, probably due to alternative conformations of the overall structure of the domain. Infection of mice showed that the recombinant coxsackievirus group B3 mutant which completely lacked the Z domain was less virulent. Pancreatic tissues from mice infected with wild-type virus and recombinant virus were equally affected. However, the heart tissue from mice infected with the recombinant virus showed only slight signs of myocarditis. These results suggest that the enterovirus B-like-specific Z domain plays a role in coxsackievirus-induced pathogenesis.