(For a Reuters live blog on U.S., UK and European stock

markets, click or type LIVE/ in a news window)

*

Spirit Aero up following report of Boeing ( BA ) nearing buyout

deal

*

Sarepta surges on expanded use of gene therapy

*

Gilead gains after long-acting HIV drug trial success

*

Futures: Dow, S&P 500, Nasdaq flat

(Updated at 7:29 a.m. ET)

By Lisa Pauline Mattackal and Ankika Biswas

June 21 (Reuters) - U.S. stock index futures were little

changed on Friday as megacap tech and chip stocks lost ground,

with investors awaiting manufacturing and services sectors

surveys for more clues on the health of the world's largest

economy.

The S&P 500 crossed the 5,500 point milestone during

Thursday's session, however, both the benchmark index and the

tech-heavy Nasdaq closed lower as megacap stocks pulled

back.

AI chip firm Nvidia ( NVDA ) dropped 1.4% in premarket

trading on Friday, after losses in the previous session saw its

market valuation fall back below that of Microsoft ( MSFT ).

Semiconductor stocks Qualcomm ( QCOM ), Micron Technology ( MU )

and Arm Holdings were down between 1% and 2%,

while megacaps such as Microsoft ( MSFT ) and Meta Platforms ( META )

were down around 0.3% each.

Wall Street's bumper gains since the final leg of 2023 has

been primarily driven by the likes of Nvidia ( NVDA ) and a handful of

other heavily weighted stocks linked to artificial intelligence.

Analysts, however, have flagged whether the strong increase in

their valuations is sustainable.

Investors are also assessing a string of weakening economic

data and commentary from the U.S. Federal Reserve officials that

interest rates could remain higher for longer if there is no

consistent improvement in inflation numbers.

Later in the day, focus will be on flash S&P PMI readings,

that are expected to fall slightly, but remain above the 50

level that shows activity is still expanding.

"Any unexpected slowdown in the U.S. economy could spark

some jitters ... but investors will be hoping to see a

moderation in price pressures, which would be positive for risk

sentiment," said Raffi Boyadjian, lead investment analyst at

forex broker XM.

Friday's session will also mark the expiry of quarterly

derivatives contracts tied to stocks, index options and futures,

also known as "triple witching".

"With Wall Street hit by profit taking after almost

uninterrupted gains during June, there is a risk of some further

volatility on Friday because of triple witching," Boyadjian

said.

All three major Wall Street stock indexes are set to close

the week higher, as is the small-cap focused Russell 2000

.

Money markets are pricing in a 58% chance of a 25-basis

point interest rate cut at the Fed's meeting in September, and

still expect about two rate cuts this year, according to LSEG's

FedWatch data.

At 7:29 a.m. ET, Dow e-minis were up 7 points, or

0.02%, S&P 500 e-minis were down 1.75 points, or 0.03%,

and Nasdaq 100 e-minis were up 2.25 points, or 0.01%.

Spirit AeroSystems ( SPR ) jumped 4.2% following a Reuters

report that Boeing ( BA ) is nearing a deal to buy back the

airplane parts supplier after months of talks.

Drugmaker Gilead jumped 2.9%, extending gains from

Thursday as a late-stage study showed its long-acting injectable

drug was more effective in preventing HIV infection in women

compared to its existing daily pill Truvada.

Sarepta Therapeutics ( SRPT ) soared 37.1% after the U.S.

Food and Drug Administration allowed the expanded use of the

company's gene therapy for patients with Duchenne muscular

dystrophy aged four and older.