The study consists of 2 parts: Part A is a randomized, multiple-dose, double-blind, placebo-controlled sequential dose escalation study to evaluate GS-6624 in subjects with Idiopathic Pulmonary Fibrosis (IPF) and was completed in October 2011.

Part B is a randomized, two-dose, open-label dose expansion study to evaluate GS-6624 in subjects with IPF and is currently enrolling.

The primary objective of this study is to characterize the safety, tolerability, and PK of GS-6624 after multiple IV administrations in patients with IPF. The secondary objectives are to evaluate the formation of anti-GS-6624 antibodies and to measure the effects of GS-6624 on FVC, DLCO, and SGRQ score. A total of 48 patients will be enrolled. In the double-blind phase (Part A), a total of 18 patients were enrolled at 3 dose levels. Part A was completed in October 2011.

In Part B, 30 patients will be enrolled at 2 dose levels. Part B is open-label and is currently enrolling.

Inclusion Criteria:

1. Acceptable results on pulmonary function tests
2. At rest oxygen saturation ≥90% on room air
3. Adequate organ function

Exclusion Criteria:

1. High resolution computer tomography pattern showing emphysema that is greater than fibrosis
2. Acceptable results on whole body plethysmography
3. History of clinically significant hepatic or renal disease
4. Poorly controlled or severe diabetes mellitus
5. Use of systemic immunosuppressants within 28 days of GS-6624 infusion