Round optimization for improved discovery of native bispecific antibodies

The assembly of bispecific antibodies (bsAb) that retain the structure of a standard IgG can be challenging as the correct pairing of the different heavy and light chains has to be ensured while unwanted side products kept to a minimum. The use of antibodies sharing a common chain facilitates assembly of such bsAb formats but requires additional efforts during the initial discovery phase. We have developed a native bsAb format called κλ body based on antibodies that, while being specific for different antigens, share the same heavy chain. Such antibodies can readily be isolated from antibody libraries incorporating a single VH combined with light chain diversity. However, in order to improve the discovery process of such fixed VH antibodies, we developed a method to optimize populations of light chains by recovering and shuffling CDRL3 sequences that have been enriched for antigen binding by phage display selection. This approach allowed for the isolation of a more diverse and potent panel of antibodies blocking the interaction between PD-1 and PD-L1 when compared to our standard in vitro selection approach, thus providing better building blocks for subsequent bsAb generation.

By-passing in vitro screening--next generation sequencing technologies applied to antibody display and in silico candidate selection

In recent years, unprecedented DNA sequencing capacity provided by next generation sequencing (NGS) has revolutionized genomic research. Combining the Illumina sequencing platform and a scFv library designed to confine diversity to both CDR3, >1.9 × 10(7) sequences have been generated. This approach allowed for in depth analysis of the library's diversity, provided sequence information on virtually all scFv during selection for binding to two targets and a global view of these enrichment processes. Using the most frequent heavy chain CDR3 sequences, primers were designed to rescue scFv from the third selection round. Identification, based on sequence frequency, retrieved the most potent scFv and valuable candidates that were missed using classical in vitro screening. Thus, by combining NGS with display technologies, laborious and time consuming upfront screening can be by-passed or complemented and valuable insights into the selection process can be obtained to improve library design and understanding of antibody repertoires.

The binding properties and biological activities of Bcl-2 and Bax in cells exposed to apoptotic stimuli

The oncogene product Bcl-2 protects cells from apoptosis whereas its homolog Bax functions to kill cells. Several binding partners of Bcl-2 and Bax have been isolated, but none of them has yet provided clues as to exactly how Bcl-2 and Bax work. According to one view, Bcl-2 and Bax interact with survival and death effector molecules, respectively, and neutralize each other through heterodimerization. Alternatively, Bcl-2 requires Bax for death protection, and additional proteins bind to the heterodimer to regulate its activity. Here we used a co-immunoprecipitation strategy to distinguish between these two possibilities. We show that the Bcl-2-Bax heterodimer is maintained, and no other protein associates stably in detectable amounts with Bcl-2, Bax, or the heterodimer in anti-Bcl-2 and anti-Bax immunoprecipitates from normal cells and cells exposed to apoptotic stimuli. Analysis of cells expressing various levels of Bcl-2 and Bax, however, revealed that the degree of protection against apoptosis does not correlate with the number of Bcl-2-Bax heterodimers but the amount of Bcl-2 that is free of Bax. In addition, the survival activity of Bcl-2 is unaffected when Bax expression is ablated by an antisense strategy. Our findings suggest that the Bcl-2-Bax heterodimer is a negative regulator of death protection, and that Bcl-2 requires neither Bax nor major, stable interactions with other cellular proteins to exert its survival function. We therefore propose that Bcl-2 acts as an enzyme (capturing substrates in a transient way), as a homodi- or multimer, or through the interaction with non-proteaceous targets (lipids, ions).

The influence of EDTMP-concentration on the biodistribution of radio-lanthanides and 225-Ac in tumor-bearing mice. The ISOLDE Collaboration

High-resolution gamma spectroscopy was applied to measure simultaneously the biodistribution of carrier-free radionuclides of several lanthanides (141Ce, 145Sm, 149Gd, 167Tm) and 225Ac in tumor-bearing nude mice. Mixtures of the radiotracers were injected in solutions containing different concentrations of EDTMP (ethylenediaminetetramethylenephosphonic acid). The strong dependence of liver uptake on the ionic radius of the radio-lanthanides was confirmed for all tracers used. The ratios of radioactivity concentrated in tumour that concentrated in liver are strongly influenced by the EDTMP concentration, reaching values close to 10 for Tm, 3 for Sm, and 1 for Ac. The optimal EDTMP concentrations, giving highest tumor-to-liver ratios of enrichment, were between 1 and 10 mM for 100 microL injected volume for the animal model used in this experiment. In radionuclide therapy using EDTMP as ligands, close control of ligand concentration will be necessary.

Bcl-2 overexpression blocks activation of the death protease CPP32/Yama/apopain

The C. elegans gene product ced-9 inhibits programmed cell death by negatively regulating the death-mediating protease ced-3. The mammalian homolog of ced-9 is the oncoprotein Bcl-2. Overexpression of Bcl-2 spares mammalian and nematodal cells from dying and prevents ectopic cell death in ced-9 loss-of-function mutants. Although Bcl-2 has been shown to act as an antioxidant under certain conditions, additional functions have emerged from studies under low oxygen pressure. Here we show that Bcl-2 overexpression impairs activation of the interleukin-1beta converting enzyme-related death protease CPP32/Yama/apopain, the mammalian homolog of ced-3. When U937 monocytes undergo programmed cell death in response to tumor necrosis factor alpha, the inactive CPP32 precursor is cleaved into its active forms. As a consequence poly(ADP ribose) polymerase, a major substrate of CPP32, is faithfully cleaved into a 85 kD fragment. Bcl-2 overexpressing cells are protected from tumor necrosis factor alpha-induced death and display neither CPP32 maturation nor PARP cleavage. The inhibitory effect of Bcl-2 on CPP32 activation is indirect since no physical interaction between the two proteins could be detected. These results indicate that Bcl-2 neutralizes an unknown cellular activator of CPP32 to save cells from programmed cell death.