Paul D. Rennert

B7-1 and B7-2 do not deliver identical costimulatory signals, since B7-2 but not B7-1 preferentially costimulates the initial production of IL-4

The functional necessity for two CD28 counterreceptors (B7-1 and B7-2) is presently unknown. B7-1 and B7-2 equivalently costimulate IL-2 and interferon-gamma (IFN gamma) production and IL-2 receptor alpha and gamma chain expression. B7-2 induces significantly more IL-4 production than B7-1, with the greatest difference seen in naive T cells. Repetitive costimulation of CD4+ CD45RA+ T cells with B7-2 results in moderate levels of both IL-4 and IL-2, whereas repetitive costimulation with B7-1 results in high levels of IL-2 and low levels of IL-4. Therefore, B7-1 and B7-2 costimulation mediate distinct outcomes, since B7-2 provides an initial signal to induce naive T cells to become IL-4 producers, thereby directing the immune response more towards Th0/Th2, whereas B7-1 is a more neutral differentiative signal.

Combination cancer immunotherapy and new immunomodulatory targets

Targeting immune checkpoints such as programmed cell death protein 1 (PD1), programmed cell death 1 ligand 1 (PDL1) and cytotoxic T lymphocyte antigen 4 (CTLA4) has achieved noteworthy benefit in multiple cancers by blocking immunoinhibitory signals and enabling patients to produce an effective antitumour response. Inhibitors of CTLA4, PD1 or PDL1 administered as single agents have resulted in durable tumour regression in some patients, and combinations of PD1 and CTLA4 inhibitors may enhance antitumour benefit. Numerous additional immunomodulatory pathways as well as inhibitory factors expressed or secreted by myeloid and stromal cells in the tumour microenvironment are potential targets for synergizing with immune checkpoint blockade. Given the breadth of potential targets in the immune system, critical questions to address include which combinations should move forward in development and which patients will benefit from these treatments. This Review discusses the leading drug targets that are expressed on tumour cells and in the tumour microenvironment that allow enhancement of the antitumour immune response.

Defining critical residues m the epitope for a hiv-neutralizing monoclonal antibody using phage display and peptide array technologies

A peptide display library [Scott and Smith, Science 249 (1990) 386-390] was constructed that expressed 1.5 x 10(8) unique 20-amino-acid (aa) peptides fused to the N-terminus of the pIII coat protein of filamentous phage fd. This phage display library (PDL-20) was prepared using a degenerate oligodeoxyribonucleotide designed to minimize bias towards most aa. Characterization of the PDL-20 showed that all aa were present at the expected frequency and that there was no positional bias. Screening of this library with a HIV-1 isotype MN envelope reactive monoclonal antibody (mAb 58.2) using two different panning procedures showed that the biopanning technique was sensitive to one phage in 10(8). Analysis of peptide sequences from panning the mAb identified a core antibody recognition sequence of four aa residues (GPGR) and two preferred flanking residues on either side. This epitope occurred at various locations within the random aa segment demonstrating an absence of positional or nearest neighbor effects. Parallel panning experiments using an array of 266 synthetic peptides identified an epitope similar to that defined by the phage display library.

Genomic organization of the gene coding for the costimulatory human B-lymphocyte antigen B7-2 (CD86)

The generation of an antigen-specific T-cell response requires that the T lymphocyte receive two signals from the antigen presenting cell. The specificity of this response is provided by antigen presented to the T lymphocyte and involves stimulation of the T lymphocyte via the T-cell receptor (TCR)/CD3 complex. The second, or costimulatory signal, can be provided by ligation of the B-lymphocyte activation antigens B7-1 (CD80) and B7.2 (CD86) to TCR antigen CD28. The cDNAs for both CD80 and CD86 have been isolated and are predicted to encode type 1 membrane proteins of the immunoglobulin (Ig) superfamily. The predicted protein is composed of a signal peptide followed by two Ig-like extracellular domains, a transmembrane domain, and a cytoplasmic tail. Here we report that the genomic organization of CD86 reflects its functional structure, and is similar to that oound for CD80. The gene is composed of eight exons which span more than 22 kilobases. The predicted protein functional domains of signal peptide, extracellular IgV- and Ig-like regions, and transmembrane domain coincide with the genomic structure. Two independent sequences had been reported for CD86 cDNA which differed in their 5′-untranslated (UT) regions. We find CD86 exons 1 and 2 correspond to these alternate 5′UT sequences. Splicing of exon 1 or 2 with the signal peptide encoding exon 3 would produce mRNA transcripts complementary to the reported cDNA clones. Exons 4 and 5 correspond to IgV- and IgC-like extracellular domains, respectively. Exon 6 encodes the transmembrane region and beginning of the cytoplasmic tail. Exons 7 and 8 encode the remainder of the cytoplasmic tail and 3′UT sequences.