A novel in vitro vaccine booster strategy could lead to faster production of human monoclonal antibodies (mAbs) and shorten vaccine development by speeding evaluation of antigens, according to researchers. In a paper published in the Journal of Experimental Medicine on July 24, 2017, an international group of researchers led by Facundo Batista, PhD, associate director of the Ragon Institute of Massachusetts General Hospital, Harvard, and MIT, described a method to stimulate human memory B cells to produce antigen-specific antibodies.
When stimulated by an infection or vaccine, the immune system’s B-cells respond to antigens by signaling through their surface B cell receptors (BCRs), setting off a cascade that spurs proliferation and secretion of antibody-producing plasma cells. “Plasma cells are the antibody factories,” Batista told GEN.
But generating antibodies in vitro from patient blood is difficult because the B cells need to be primed with an additional signal such as CD40 or TLR and to be dosed with different interleukin cocktails. Laboratory methods for isolating antibodies, including phage display, EBV immortalization, yeast display, and humanized animal models, all depend on large-scale screening to identify specific antibodies. Techniques like antigen-specific B cell sorting and single cell cloning have improved antibody identification, but only work on high-affinity antibodies.
Batista’s team exposed B cells derived from healthy patient blood to “a cocktail of nanoparticles” attached to an antigen and CpG oligodeoxynucleotides (CpG), which are DNA fragments that can activate the TLR9 signaling protein when integrated into a cell.
“There is only one trick there,” says Batista. Introducing CpG alone in solution will activate the B cells indiscriminately. “But the cells you are interested in, they are one in 10,000, one in 100,000; how do you identify them?” asked Batista. “If you attach the ligand together with a protein to a nanoparticle, the TLR ligand becomes refractory to the cell, unless you internalize it through the B cell receptor. And the only cells that do that are the cells that are able to bind the protein on the nanoparticle. I am exploiting the capacity of the B cell receptor to capture what is outside the cell and bring it in. Because the TLR receptors are inside the cell, they only get exposed to the ligand when the B cell brings it to them.”
The Batista team was able to produce a large panel of high affinity human mAbs within a few days. Then, taking memory B cells derived from healthy donors that had not been previously exposed to that particular antigen, they validated their results in successive experiments using a gp120 protein on the surface of the HIV envelope, multiple strains of the H1N1 Influenza A virus, as well as antigens of tetanus.
According to Batista, a limitation of the study was that it did not produce a complete immune response in culture. A next step is to enable affinity maturation in vitro. Batista’s personal mission is to develop an HIV treatment—but in the meantime, this technique could provide quicker immunity testing as well as generate mAbs in vitro without needing human clinical trials.
