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LONDON (Reuters) - Two shareholder advisory firms have backed Takeda Pharmaceutical's 4502.T $62 billion takeover offer for drugmaker Shire SHP.L, dealing a blow to a group of investors who hope to block the deal.

Institutional Shareholder Services (ISS) and Glass Lewis both recommended on Tuesday that shareholders in Japan’s Takeda vote for the acquisition at an investor meeting scheduled for Dec. 5, at which the pharmaceuticals company needs to secure two-thirds support.

It is a boost for Takeda, which has faced a campaign by a small group of about 130 retail investors that includes former employees to derail the takeover of London-listed Shire.

Those shareholders are worried about the significant debt that Takeda is taking on to complete the deal and the risks posed by the scale of the acquisition, which is the largest-ever overseas acquisition by a Japanese company.

But ISS and Glass Lewis said that investor support for the cash-and-shares transaction was warranted.

“The deal diversifies the company in terms of products and geographies, and provides strong cash flow generation that, combined with divestments, allows for relatively rapid deleveraging, despite maintaining top of the range leverage in the mid-term,” ISS said in a report to clients.

Glass Lewis said in a separate report that “the strategic case is compelling for Takeda.”

Shares in Shire were up 0.4 percent in London while Takeda closed up 0.6 percent in Tokyo.