Severe Neutropenia

My husband (51M, white) was diagnosed with follicular lymphoma in 2022. At the time his WBC and neutrophils were low. Once he started treatments, his WBC and neutrophils could never recover enough for him to maintain chemo treatments and go into remission. He then had CAR-T, which put him into remission. His WBC and neutrophils never reached normal levels. Lymphoma returned last year. Same issue with treatment and WBC and neutrophils. He halted treatments, but fortunately was in remission despite that. He has been hospitalized three times in the 45 days for neutropenic fevers and pneumonia. He is home now, but WBC is 1.2 and absolute neutrophils are 0.1. We have tried daily shots that do nothing. We are trying to get Neulasta shots approved because nothing else is working. All tests have come back negative. They have looked for autoimmune issues. Has anyone ever encountered this type of neutropenia?