Combine the given two facts to write a concluding fact. Note that there should be some parts of the first and second facts that are not mentioned in this conclusion fact. Your combined fact should be the result of a chain between the two facts. Chains form when two facts connect together to produce a concluding fact. An example of a chain is: "pesticides cause pollution" (fact1) + "pollution can harm animals" (fact2) → "pesticides can harm animals" (conclusion fact). Parts of the concluding fact overlap with the first and the second fact. To construct such a  concluding fact, a useful way is to borrow the subject from one fact and the ending conclusions from another fact.

Fact 1: HIV infects and destroys helper T cells. 
Fact 2: Helper T cells are the critical link in our immune system.
HIV damages our immune system.

Fact 1: Female gametophytes produce eggs inside the ovaries of flowers. 
Fact 2: Gametophytes are the parent of the baby fern.
Female flower parents produce eggs inside the ovaries of flowers.

Fact 1: Antigens are molecules that the immune system recognizes as foreign to the body. 
Fact 2: Antigens are expressed by cancer cells.

the immune system can recognize cancer as foreign to the body.