LFA-1 activation enriches tumor-specific T cells in a cold tumor model and synergizes with CTLA-4 blockade

The inability of CD8⁺ effector T cells (Teffs) to reach tumor cells is an important aspect of tumor resistance to cancer immunotherapy. The recruitment of these cells to the tumor microenvironment (TME) is regulated by integrins, a family of adhesion molecules that are expressed on T cells. Here, we show that 7HP349, a small-molecule activator of lymphocyte function–associated antigen-1 (LFA-1) and very late activation antigen-4 (VLA-4) integrin cell-adhesion receptors, facilitated the preferential localization of tumor-specific T cells to the tumor and improved antitumor response. 7HP349 monotherapy had modest effects on anti–programmed death 1–resistant (anti–PD-1–resistant) tumors, whereas combinatorial treatment with anti–cytotoxic T lymphocyte–associated protein 4 (anti–CTLA-4) increased CD8⁺ Teff intratumoral sequestration and synergized in cooperation with neutrophils in inducing cancer regression. 7HP349 intratumoral CD8⁺ Teff enrichment activity depended on CXCL12. We analyzed gene expression profiles using RNA from baseline and on treatment tumor samples of 14 melanoma patients. We identified baseline CXCL12 gene expression as possibly improving the likelihood or response to anti–CTLA-4 therapies. Our results provide a proof-of-principle demonstration that LFA-1 activation could convert a T cell–exclusionary TME to a T cell–enriched TME through mechanisms involving cooperation with innate immune cells.

Magnetic Resonance Imaging of Atherosclerotic Plaque at Clinically Relevant Field Strengths (1T) by Targeting the Integrin α4β1

Inflammation drives the degradation of atherosclerotic plaque, yet there are no non-invasive techniques available for imaging overall inflammation in atherosclerotic plaques, especially in the coronary arteries. To address this, we have developed a clinically relevant system to image overall inflammatory cell burden in plaque. Here, we describe a targeted contrast agent (THI0567-targeted liposomal-Gd) that is suitable for magnetic resonance (MR) imaging and binds with high affinity and selectivity to the integrin α4β1(very late antigen-4, VLA-4), a key integrin involved in recruiting inflammatory cells to atherosclerotic plaques. This liposomal contrast agent has a high T1 relaxivity (~2 × 10⁵ mM^-1s^-1 on a particle basis) resulting in the ability to image liposomes at a clinically relevant MR field strength. We were able to visualize atherosclerotic plaques in various regions of the aorta in atherosclerosis-prone ApoE^-/- mice on a 1 Tesla small animal MRI scanner. These enhanced signals corresponded to the accumulation of monocyte/macrophages in the subendothelial layer of atherosclerotic plaques in vivo, whereas non-targeted liposomal nanoparticles did not demonstrate comparable signal enhancement. An inflammatory cell-targeted method that has the specificity and sensitivity to measure the inflammatory burden of a plaque could be used to noninvasively identify patients at risk of an acute ischemic event.

Small molecule agonist of very late antigen-4 (VLA-4) integrin induces progenitor cell adhesion

Activation of the integrin family of cell adhesion receptors on progenitor cells may be a viable approach to enhance the effects of stem cell-based therapies by improving cell retention and engraftment. Here, we describe the synthesis and characterization of the first small molecule agonist identified for the integrin α4β1 (also known as very late antigen-4 or VLA-4). The agonist, THI0019, was generated via two structural modifications to a previously identified α4β1 antagonist. THI0019 greatly enhanced the adhesion of cultured cell lines and primary progenitor cells to α4β1 ligands VCAM-1 and CS1 under both static and flow conditions. Furthermore, THI0019 facilitated the rolling and spreading of cells on VCAM-1 and the migration of cells toward SDF-1α. Molecular modeling predicted that the compound binds at the α/β subunit interface overlapping the ligand-binding site thus indicating that the compound must be displaced upon ligand binding. In support of this model, an analog of THI0019 modified to contain a photoreactive group was used to demonstrate that when cross-linked to the integrin, the compound behaves as an antagonist instead of an agonist. In addition, THI0019 showed cross-reactivity with the related integrin α4β7 as well as α5β1 and αLβ2. When cross-linked to αLβ2, the photoreactive analog of THI0019 remained an agonist, consistent with it binding at the α/β subunit interface and not at the ligand-binding site in the inserted ("I") domain of the αL subunit. Co-administering progenitor cells with a compound such as THI0019 may provide a mechanism for enhancing stem cell therapy.

Purification and characterization of avian beta 1,4 galactosyltransferase: comparison with the mammalian enzyme

Avian beta 1,4 galactosyltransferase (GalTase) was purified from chicken serum, partially characterized and compared to mammalian GalTase using antibody cross-reactivity, Northern blot hybridization and amino acid sequence analysis. The enzyme was purified to apparent homogeneity by alpha-lactalbumin(LA)-agarose affinity chromatography followed by preparative SDS-polyacrylamide gel electrophoresis, and identified as two proteins of apparent molecular masses of 39 and 46 kD. Chicken serum GalTase had a Km for UDPGal of 42 microM, for GlcNAc of 10 mM and had optimal activity in the presence of 10-20 mM MnCl2. Substrate and linkage specificity analyses indicated that the purified enzyme behaves as a traditional Gal beta 1,4 GlcNAc:GalTase, since: (i) the avian beta 1,4 GalTase bound to alpha-LA; (ii) terminal GlcNAc residues served as good acceptors for chicken serum GalTase; (iii) the enzyme was inhibited by high concentrations of GlcNAc; (iv) the galactosylated product was sensitive to beta 1,4-specific beta-galactosidase. Finally, the disaccharide reaction product comigrated with authentic beta 1,4 N-acetyllactosamine standard. No other GalTase activities were detectable using a battery of defined glycoside substrates. Polyclonal antibodies raised against the two gel-purified GalTase proteins showed reactivity with avian GalTase by ELISA and immunoprecipitation assays. The antibodies also inhibited GalTase activity toward both high mol. wt and monosaccharide acceptor substrates. Despite similar kinetics and substrate specificity, the avian and mammalian GalTases showed little overall structural similarity, since polyclonal anti-avian GalTase IgG failed to react with mammalian GalTase purified from bovine milk, and conversely anti-bovine milk GalTase IgG did not react with the avian enzyme. Furthermore, in Northern blot analysis, no hybridization was detected when chicken embryo liver poly(A)+ RNA was probed with a mouse GalTase cDNA, even under conditions of reduced stringency. Amino acid sequence analysis identified three of five tryptic peptides that are homologous to the mammalian sequence within a putative substrate binding domain and the carboxy terminal domain of the enzyme. Their overall structural disparity leads us to believe that regions of homology between the avian and mammalian GalTases may represent active sites of the enzyme.

Amplification and molecular cloning of the hamster tunicamycin-sensitive N-acetylglucosamine-1-phosphate transferase gene. The hamster and yeast enzymes share a common peptide sequence

The first step in the assembly of the dolichol-linked oligosaccharides required for asparagine-linked glycosylation in eukaryotes is catalyzed by a tunicamycin-sensitive, dolichol phosphate-dependent N-acetylglucosamine-1-phosphate transferase (GPT). A fragment of the gene encoding the enzyme from Chinese hamster ovary (CHO) cells was partially cloned and characterized by a novel strategy. By stepwise selection, CHO cells were made 80-fold resistant to tunicamycin and found to have 10-fold elevated levels of GPT activity. Using a cloned segment of the yeast ALG-7 gene, which encodes the putative GPT from yeast, an amplified gene was identified by Southern blotting of the CHO DNA and a 6.6-kilobase segment of the gene was molecularly cloned. A family of RNA molecules in the 2.0-2.2-kilobase range identified with a probe from this gene was overexpressed in the resistant cells. The cloned DNA revealed a 24-amino acid residue sequence that was 92% conserved with the corresponding yeast sequence.