Transforming a customer-provided custom cell line typically involves introducing a foreign DNA sequence, such as a plasmid, into the cells to modify their genetic makeup. This can be accomplished using a variety of methods, including transfection, electroporation, or viral transduction.

The specific method used will depend on the type of cell line, the desired level of transfection efficiency, and the nature of the foreign DNA sequence. For example, some cell lines are more amenable to transfection than others, and viral transduction may be required for certain types of DNA sequences.

Once the foreign DNA sequence has been successfully introduced into the cells, the cells can be selected for using a variety of selection markers, such as antibiotic resistance genes. This allows for the isolation of cells that have incorporated the foreign DNA sequence and enables the production of stable cell lines.

Transforming a custom cell line can be a complex process that requires careful planning and optimization. It is often carried out by experienced molecular biologists or specialized service providers.