The parent comment mentioned existing therapies. As in drugs like Humira, PD-1 inhibitors, PCSK9 inhibitors. No doubt they are complex to produce. But I was doubting that the costs of production are the reason why these drugs are expensive. Companies will charge what payers will pay. See Humira [1]: many times more costly in the US than in the UK.

1: https://en.m.wikipedia.org/wiki/Adalimumab