This is a research study to evaluate if the oral medication doxycycline can slow lung damage caused by emphysema in people who also have HIV. This study will also evaluate the safety and tolerability of doxycycline.

Doxycycline is an antibiotic that was originally approved by the U.S. Food and Drug Administration (FDA) in 1967 to treat or prevent a variety of infections and conditions including bronchitis, pneumonia, certain genital infections, Lyme disease, and malaria. Because doxycycline has not been approved by the FDA to treat emphysema in people living with HIV, the use of the drug in this study is considered investigational.

Participants will be randomly assigned (like the flip of a coin) to receive either doxycycline or placebo. A placebo is a capsule that looks like doxycycline but does not contain any active medication. Participants and study staff cannot choose which drug each individual receives and there is a 50/50 chance of being assigned either option.

Participation in this study includes about 10 study visits, which may consist of chest CT scans, pulmonary function tests, walk tests, and other lab work. Participants will receive compensation for each study visit they complete.