Using MABs can show how complex the immune system is, with finely tuned balances and opposing effects. For example, TNFα may have an immunosuppressive activity itself as disease symptoms can paradoxically increase for a small number of patients using a TNFα blocking MAB. People taking TNF-antagonists are more susceptible to serious infection, and may see tuberculosis or hepatitis B reactivated.^4,9

While rare, more cases of malignancies including lymphoma have been observed among patients receiving a TNF-antagonist compared with control patients, and leukaemia has occurred in patients using TNF-antagonists.⁴

EGFR inhibitor use has been linked with keratitis and ulcerative keratitis. In rare cases, this has resulted in corneal perforation and blindness.²

Perhaps a more unusual consideration is that some helminth infections may involve IgE or eosinophil activity, and using a MAB may upset the immune response increasing the risk of parasite activity. Patients with a pre-existing helminth infestation should be treated for this before starting a MAB such as mepolizumab for conditions including eosinophilic asthma, or omalizumab for allergic asthma.⁴