An anti-CTLA-4 heavy chain-only antibody with enhanced Treg depletion shows excellent preclinical efficacy and safety profile.

The value of anti-CTLA-4 antibodies in cancer therapy is well established. However, the broad application of currently available anti-CTLA-4 therapeutic antibodies is hampered by their narrow therapeutic index. It is therefore challenging and attractive to develop the next generation of anti-CTLA-4 therapeutics with improved safety and efficacy. To this end, we generated fully human heavy chain-only antibodies (HCAbs) against CTLA-4. The hIgG1 Fc domain of the top candidate, HCAb 4003-1, was further engineered to enhance its regulatory T (Treg) cell depletion effect and to decrease its half-life, resulting in HCAb 4003-2. We tested these HCAbs in in vitro and in vivo experiments in comparison with ipilimumab and other anti-CTLA4 antibodies. The results show that human HCAb 4003-2 binds human CTLA-4 with high affinity and potently blocks the binding of B7-1 (CD80) and B7-2 (CD86) to CTLA-4. The results also show efficient tumor penetration. HCAb 4003-2 exhibits enhanced antibody-dependent cellular cytotoxicity function, lower serum exposure, and more potent anti-tumor activity than ipilimumab in murine tumor models, which is partly driven by a substantial depletion of intratumoral Tregs. Importantly, the enhanced efficacy combined with the shorter serum half-life and less systemic drug exposure in vivo potentially provides an improved therapeutic window in cynomolgus monkeys and preliminary clinical applications. With its augmented efficacy via Treg depletion and improved safety profile, HCAb 4003-2 is a promising candidate for the development of next generation anti-CTLA-4 therapy.

Ser(262) determines the chloride-dependent colour tuning of a new halorhodopsin from Haloquadratum walsbyi.

Light is an important environmental signal for all organisms on earth because it is essential for physiological signalling and the regulation of most biological systems. Halophiles found in salt-saturated ponds encode various archaeal rhodopsins and thereby harvest various wavelengths of light either for ion transportation or as sensory mediators. HR (halorhodopsin), one of the microbial rhodopsins, senses yellow light and transports chloride or other halides into the cytoplasm to maintain the osmotic balance during cell growth, and it exists almost ubiquitously in all known halobacteria. To date, only two HRs, isolated from HsHR (Halobacterium salinarum HR) and NpHR (Natronomonas pharaonis HR), have been characterized. In the present study, two new HRs, HmHR (Haloarcula marismortui HR) and HwHR (Haloquadratum walsbyi HR), were functionally overexpressed in Escherichia coli, and the maximum absorbance (λmax) of the purified proteins, the light-driven chloride uptake and the chloride-binding affinity were measured. The results showed them to have similar properties to two HRs reported previously. However, the λmax of HwHR is extremely consistent in a wide range of salt/chloride concentrations, which had not been observed previously. A structural-based sequence alignment identified a single serine residue at 262 in HwHR, which is typically a conserved alanine in all other known HRs. A Ser262 to alanine replacement in HwHR eliminated the chloride-independent colour tuning, whereas an Ala246 to serine mutagenesis in HsHR transformed it to have chloride-independent colour tuning similar to that of HwHR. Thus Ser262 is a key residue for the mechanism of chloride-dependent colour tuning in HwHR.