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By Deena Beasley

Oct 24 (Reuters) - Gilead Sciences Inc on Thursday posted third-quarter results largely in line with Wall Street estimates, led by higher HIV drug sales, but sales of cancer cell therapy Yescarta fell slightly from the previous quarter.

On an adjusted basis, the drugmaker posted a profit of $1.75 a share, one cent higher than the average Wall Street estimate, according to IBES data from Refinitiv.

Including $3.9 billion in expenses from a previously announced investment in European biotech Galapagos NV, California-based Gilead had a net loss for the quarter of $1.2 billion, or 92 cents a share.

Gilead's shares, which closed at $66 in regular trading, were down 1.5% after hours.

Quarterly sales of HIV drugs, which accounted for more than three-fourths of total sales, rose to $4.2 billion from $3.7 billion a year earlier.

Sales of Yescarta, part of a new class of therapies that require altering immune system cells to fight cancer, totaled $118 million, short of analyst expectations, and down 2% from the second quarter.

Use of the one-time treatment, priced at $373,000 in the United States, has been slow to ramp up due to a variety of issues, including high hospital costs.

Investors are keen to see how Gilead can expand into other therapeutic areas under Chief Executive Officer Daniel O’Day, a Roche veteran who took charge in March.

On a conference call the CEO said Gilead is confident in Yescarta and will present updated survival and other data at a medical meeting in December. He pledged to say more in coming months about oncology plans, both "outside of cell therapy and complementary to cell therapy."

Gilead, in partnership with Galapagos, is preparing for the launch in Europe of filgotinib as a treatment for rheumatoid arthritis. It plans to file for U.S. approval of filgotinib before the end of this year.

Quarterly hepatitis C sales fell to $674 million from $902 million as patients have been cured of the liver-damaging virus and rival products have emerged. Also, Gilead this year launched its own generic hepatitis C drugs in an effort to lower list prices to match the discounts that large buyers receive for branded products.

Total revenue for the quarter was flat at $5.6 billion.

"Gilead reported a relatively underwhelming albeit in-line third quarter," JP Morgan analyst Cory Kasimov said in research note.

The company narrowed its full-year sales outlook to between $21.8 billion and $22.1 billion from a previous $21.6 billion to $22.1 billion.

(Reporting by Deena Beasley Editing by Bil Berkrot and Lisa Shumaker)