Highly read on www.pnas.org in December

Algae could be used to make complex, targeted cancer drugs, thanks to their photosynthetic organelles, the chloroplasts.

Immunotoxins are drugs that combine a toxin with an antibody; the antibody targets the toxin to specific cells, such as cancer cells. However, the drugs have proved difficult and expensive to produce. Stephen Mayfield and his colleagues at the University of California, San Diego, reasoned that the green alga Chlamydomonas reinhardtii could be used to produce immunotoxins. The chloroplasts of this alga contain the machinery to properly fold complex proteins — such as antibodies — and can tolerate some toxins.

The team used the alga to produce an antibody to CD22 — a protein found on a type of immune cell called a B cell — coupled to a bacterial toxin. The immunotoxin killed B cells in culture, and inhibited the growth of human B-cell tumours that had been implanted in mice.

Proc. Natl Acad. Sci. USA 110, E15–E22 (2013)