I don't understand the question. Antibody development starts with germline VDJ/VJC rearrangement. Then it's T cell help to push for IgG, IgA and IgE isotypes.

B cells are formed from multipotent hematopoietic stem cells in the bone marrow. The original stem cell does not contain any functional antibody genes - each cell generates a unique pair of light and heavy chains by genetic recombination of V, (D), J and C segments on their DNA. See: https://en.wikipedia.org/wiki/Antibody , paragraph "V(D)J recombination" and following. Cells that do not succeed in producing a viable combinatioon get eliminated. While the sequence of complementarity determining regions CDR1 and CDR2 are encoded on the V-segments, hypervariable CDR3 is located where the different genetic fragments are spliced together. As the newly formed B-cell multiply, the antibody genes are further diversified by somatic hypermutation. Through alternative splicing, the B-cells not only produce soluble antibodies, but also a membrane found form that is part of the B-cell receptor. This receptor stimulates cell sell survival and propagation when stimulated by the cognate antigen. As a result, those cells that produce high-affinity antibodies will out-compete those that do not recognize the antigen equally well.