What is the best way to recover from low WBC after chemotherapy (r-cvp for stage 2 diffuse large b-cell lymphoma) for a very elderly (85y) patient?

It depends. R-cvp is a relatively milder regimen and therefore it does not usually result in very low wbcs. In general, modest decrease in WBC is expected and is not associated with higher risk for infections unless WBC become very low with neutrophil count below 500. If this is the case, you doctor may decide to use a growth factor given after chemotherapy to stimulate your bone marrow to produced wbcs.