Low Immunoglobulins and Infection Risk — After Blood Cancer Immunotherapy

Low immunoglobulins follow B-cell-directed immunotherapy, not immunotherapy in general. Most patients with cancer in India are not candidates for any immunotherapy. Among blood cancers, only people whose cells carry the B-cell marker are given this class of treatment. If you have not had it, this page is unlikely to apply to you.

We put that first on purpose. Families often read one survivorship page and assume every warning on it is coming for them. Knowing early that a risk does not apply to you is worth as much as knowing that it does.

This is not your risk if

• You were treated with checkpoint immunotherapy for a solid tumour — that class does not deplete B cells and does not lower antibody levels. It has its own side-effect pattern, set out in Immunotherapy for Head and Neck Cancer.
• Your cells never carried the B-cell marker — most T-cell lymphomas and many myeloid leukaemias do not, so B-cell-directed treatment was never offered in the first place.
• You had surgery, radiotherapy or chemotherapy alone — chemotherapy can lower blood counts for a while, but it does not usually cause the prolonged antibody deficit described here.

This is your risk if

• You had an antibody aimed at the B-cell marker — whether given alone, alongside chemotherapy, or as maintenance treatment continued over many months.
• You had a newer B-cell-directed class — treatments that bring a T cell to the B cell deplete healthy B cells just as thoroughly, and are used mainly in relapsed disease at designated centres.
• You have myeloma or a chronic B-cell leukaemia — the disease itself lowers immunoglobulins, so the level may already be low before any treatment starts.
• You had cell therapy or a stem-cell transplant — both can leave antibody levels low for a prolonged period. CION does not provide, administer or stock CAR-T or any cell therapy product, and does not perform stem-cell transplant; where either is relevant we refer you to a designated centre and stay involved in your follow-up around it.

For the people in the second group, this is one of the most under-recognised parts of survivorship. Treatment finishes, scans are reported as good, and nobody mentions that the immune system has a specific, measurable gap in it that can persist for a year or longer. That gap is manageable once it is known about, which is the entire point of this page.

Because the treatment cannot tell a healthy B cell from a cancerous one. B cells mature into the plasma cells that make your antibodies, and antibodies are immunoglobulins. Clearing the marked cells clears antibody production with them. Steroids, chemotherapy and the blood cancer itself all push the level down further.

1. 1

   B cells are your antibody factory

   B cells mature into plasma cells, and plasma cells secrete immunoglobulins. Those antibodies are what recognise a bacterium you have met before and mark it for removal. Without them, your body meets every common germ as if for the first time.

2. 2

   The treatment targets a marker, not a cancer

   The marker the medicine is built against sits on the surface of B cells. Your cancerous B cells carry it. So do all your normal ones. The treatment removes both, and that is not a fault in it - it is how it works.

3. 3

   Antibody stock runs down slowly

   Antibodies already circulating in your blood are not destroyed by the treatment. They simply are not replaced as they are used up. That is why the level drifts down over weeks and months rather than dropping the day you start.

4. 4

   Other causes stack on top

   Steroids given with the regimen suppress antibody production. Chemotherapy in the same protocol adds to it. Myeloma and chronic B-cell leukaemias lower immunoglobulins on their own. Several causes usually overlap in the same patient.

5. 5

   IgG is the one that is measured

   Laboratories report IgG, IgA and IgM separately. IgG matters most for day-to-day protection against bacteria, so it is the number your oncologist watches. Read it against the reference range printed on your own report, because ranges differ between laboratories.

Mechanism described in line with NCCN and ESMO patient-education and survivorship material. This page describes classes of treatment and their targets, not individual products.

Typical patterns described in NCCN and ESMO survivorship guidance. Your own timeline depends on which treatment you had, how many cycles, and what else was given with it - these are not predictions for any individual patient.

Not for everyone with a low number. Replacement is considered when a low immunoglobulin level comes with repeated or severe bacterial infections, such as chest, sinus or ear infections that keep returning, or one that needed admission. A low level on its own is usually monitored rather than treated.

What follows is the framework your treating team works through. It is not a recommendation, and the option of doing none of it is a real one that should be on the table.

• The level, and the direction it is moving — one reading tells you little. Two or three over months tell you whether you are recovering, holding steady or still falling.
• Your infection history, written down — how many, how severe, whether antibiotics were needed, whether any led to admission. This carries more weight than the number.
• Whether the infections are bacterial — antibody deficiency shows up as bacterial infections of the airways. Repeated viral colds point elsewhere.
• Simpler measures first — treating each infection promptly, sometimes a preventive antibiotic, and vaccination once your team judges the timing right. Many patients need nothing beyond this.
• What replacement actually involves — an infusion in day care every three to four weeks, dosed by body weight, continued for as long as it is needed; a smaller injection under the skin is an alternative for some patients.
• Cost and coverage, before you start — replacement is a blood-derived product and it is expensive, and the amount depends on your weight, so ask for a written estimate for a full course rather than for one dose. Costs are indicative only, as of August 2026. Scheme and insurance coverage varies - check it in advance rather than after the first infusion.

Criteria for starting replacement, and for stopping it, are set out in NCCN and ESMO survivorship guidance and are applied to your individual situation by your treating oncologist. Nothing on this page is a recommendation to start or stop any treatment.

Bacterial infections of the sinuses, ears and chest are the common ones. Fever is the symptom that cannot wait. If your temperature reaches 38 degrees Celsius or higher, or you are breathless, call 1800 202 8726 now or go to the nearest emergency department. Do not wait for your next clinic appointment.

Go now, do not wait

• Temperature of 38 degrees Celsius or higher — particularly during a treatment cycle or in the weeks after one, when your white cells may also be low.
• Shaking chills, breathlessness, chest pain or confusion — these can mean an infection has spread into the bloodstream. This is an emergency department visit, not a phone consultation.
• A cough with coloured sputum that is not settling — same-day medical review, because chest infections in this group need treating early and properly.

Tell your team at the next visit

• Infections that keep coming back — three or more courses of antibiotics in a year, or the same sinus or chest infection returning as soon as a course finishes.
• Anything that takes far longer to clear than it used to — a two-week cold that becomes a six-week one is information, not bad luck.
• Any new doctor you see — tell every clinician, including a dentist, that you had B-cell-directed treatment and when it finished. It changes how they interpret a fever.

Vaccination. Inactivated vaccines are safe, but your response to them may be poor while B cells are absent, so timing matters. Teams usually wait for B cells to return before giving vaccines meant to build lasting protection. Live vaccines are avoided during B-cell-directed treatment and for a period after it. Household members being vaccinated protects you indirectly. Do not start or skip a vaccine without telling your oncologist.

Repeated chest infections left unmanaged over years can cause permanent lung damage. That is the reason this deserves attention now rather than a wait-and-see approach, even though the level itself causes no symptoms.

Five requests cover almost everything. None of them is unusual, and none is expensive. Ask for them in writing so that whoever sees you next has the same picture.

• A serum immunoglobulin level — with the date, repeated at intervals so the trend is visible rather than a single snapshot.
• A written survivorship plan — naming the class of treatment you had, when it finished, and what is being monitored.
• A vaccination schedule — what to have, what to avoid, and when the timing becomes right.
• A named person to call — with a number that works after hours, and clear instructions on what counts as an emergency.
• An infection record — keep your own list of infections and antibiotic courses. It is the single most useful thing you can bring to a consultation about replacement.

Transplant and cell therapy. If a stem-cell transplant or CAR-T cell therapy is part of your history or your plan, that care belongs at a designated centre. CION does not provide, administer or stock CAR-T or any cell therapy product, and does not perform stem-cell transplant. We refer you, and we continue to support the survivorship side around it - including this one.

Related reading

• Immunotherapy Before or After Stem Cell Transplant — how the two are sequenced, and why antibody recovery after a transplant runs to its own timetable.
• Graft-Versus-Host Disease After Transplant — the other long-running immune problem after transplant, and how it is told apart from infection.
• Immunotherapy for Head and Neck Cancer — a solid-tumour example of the checkpoint class, which does not deplete B cells and does not cause this.
• Immunotherapy at CION Cancer Clinics — the hub page, covering eligibility, marker testing, day-care administration and cost.

This page is general information and does not replace a consultation. It describes classes of treatment and their targets, not individual products, and makes no comparison between products. Whether any of it applies to you depends on your treatment history and blood results, and is a decision for your treating oncologist. Immunotherapy is administered as day care at CION centres; response-assessment PET-CT is coordinated at partner imaging centres.

Finished treatment, but still falling ill?

A 45-minute consultation, your reports read properly, and a plain answer on whether your antibody level explains it. No rushed decisions and no unnecessary tests.